The Shape of Professional Growth

by Rob Douglas, Citadel Professional Solutions

There is a lot of discussion about the shape of a professional’s knowledge. I’ve seen people who are experts in their fields, and I’ve seen people able to adapt across a variety of contexts. Models describing I-shaped, T-shaped, π-shaped, and other variations attempt to capture different combinations of specialization and breadth.

These are useful models. But I think they are missing something.

They describe the shape of what you know.

They don't do as good a job describing how that shape grows.

I think professional growth looks more like a cone.

From a Small Piece of Code to a Space Telescope

When I first started working on the Hubble Space Telescope, I was assigned to the TRANS project, part of the system responsible for transforming scientific observing proposals into actions that could ultimately be executed by the spacecraft.

My first assignments were small.

I was given relatively contained areas of code to understand and fix. At that point, that was about the right size problem for me. I could understand the behavior, make a change, and in the process begin learning how the larger system worked.

But something happens when you keep doing that.

Every new piece of code touches something else.

To understand the software, I had to understand what it was trying to accomplish. That meant understanding how astronomical observations were constructed: how exposures were organized, how observations were linked, how constraints were represented, and eventually how all of that became commands that could be executed by a spacecraft.

So the more software I learned, the more spacecraft I had to learn.

And the more spacecraft I learned, the more astronomy I had to learn.

I needed to understand how astronomers thought about their observations and what they were trying to accomplish scientifically.

My knowledge wasn't just getting deeper.

It was getting wider.

Years later, I led development of the Astronomer's Proposal Tool for the James Webb Space Telescope. Some of what I had learned on Hubble transferred. A lot didn't.

Webb was a different spacecraft doing different science. I needed to understand the engineering constraints of the observatory, what was operationally possible, and how infrared astronomy differed from the visible and ultraviolet observations with which I was more familiar.

And the proposal tool wasn't an island.

Information entered there flowed into planning and scheduling. Eventually it became spacecraft commands. Those commands produced observations and data. Decisions made at the front of that chain could affect how information was represented and recombined much farther downstream.

Understanding my piece increasingly required understanding everyone else's pieces.

Then I moved into broader planning and scheduling and systems engineering leadership roles.

Now I needed to understand the architectures of multiple systems and the interfaces between them. I needed to understand how information flowed into flight operations, how those systems would be used during commissioning, and how they connected to data management and scientific operations.

Working on additional missions broadened the perspective again. I could begin separating the principles that were specific to one observatory from those that applied more generally to the business of operating space telescopes.

Eventually the learning extended well beyond engineering.

Contracts. Budgets. Planning. Project management. Organizational authority. Stakeholder management. Negotiation. Decision making. Leadership.

Each new responsibility pulled another domain into the circle.

Today, I can still go surprisingly deep into some technical aspects of these systems. But that is no longer the most valuable thing I bring to most problems.

What I increasingly bring is the ability to connect things.

I can see how the technical problem connects to the operational problem, how the operational problem connects to the organizational problem, and how all of those connect to the people who ultimately have to make the system work.

That didn't happen because I stopped being technical.

It happened because the cone kept growing.

The Problem with Being Irreplaceable

Early in your career, it is tempting to believe that the safest place to be is at the top of the I; that is, deeply specialized in something few others understand.

Become the person who knows something better than anyone else.

Become indispensable.

There is certainly value in deep expertise. Organizations need people who know difficult things deeply.

But there is a danger in deliberately making yourself irreplaceable.

If an important system depends on knowledge that exists only in your head, then you are no longer an asset—you are a liability. The organization has become dependent on you in a way that creates risk.

Good organizations eventually have to mitigate that risk through documentation, cross-training, succession planning, automation, or developing other people who can perform the work.

And if you have tied your professional self-worth to being the only person who can do something, reducing that dependency can feel like reducing your own value.

It isn't.

You can give your knowledge away without giving your value away. Your value comes from continuing to grow what you know and what you can contribute.

So I don't think the goal should be to become irreplaceable. The goal should be to become increasingly valuable.

And those are not the same thing.

From the I to the T and Beyond

The T-shaped professional improves on the I by recognizing that deep expertise becomes more useful when accompanied by breadth. The vertical stroke represents depth in a particular discipline; the horizontal stroke represents broader knowledge and the ability to work across disciplines.[1]

But even the T has proved somewhat constraining. Other variations have followed: π-shaped, M-shaped, comb-shaped, and others that add more vertical strokes to represent depth in multiple areas.

Those variations recognize an important limitation of the original model. Real people rarely have just one area of depth and a neat horizontal layer of general knowledge.

But adding another bar, or two, or three, doesn't really solve the problem.

All of these models still describe professional knowledge as a collection of lines: deep here, broad across these things, perhaps deep again over there. And they share another limitation that matters even more to me.

These models are useful when assembling a team. They help us understand the capabilities people bring to a project today. But they don't tell us much about how those people developed those capabilities, or who they might become tomorrow.

They are snapshots.

A career is a movie.

I'm less interested in describing the shape of someone's knowledge at a particular moment than in understanding how that shape grows over a career.

I think professional growth looks more like a cone.

The Cone-Shaped Professional

Imagine a cone. Its height represents the depth of your expertise. Its radius represents the breadth of your knowledge. Its volume represents the accumulated knowledge, experience, and perspective you can bring to a problem.

Over a career, that cone can change shape. You can grow deeper, expand wider, or do both.

As you learn the technologies adjacent to yours, the cone widens. You learn the systems around those technologies. Then the people who use those systems. Then the organizational processes that determine how those systems are built. Eventually, you may begin learning about the business environment in which the entire organization operates.

At the same time, you can continue developing greater depth in your core expertise. You can learn the nuances, exceptions, and underlying principles that separate familiarity from mastery.

The cone can grow deeper and wider.

And it doesn't have to grow evenly.

A researcher or technical specialist might develop an extraordinarily deep cone with a relatively small radius. A systems engineer might deliberately expand both. A senior organizational leader may develop tremendous breadth while accepting that it is impossible to remain at the deepest level of every technical discipline within that breadth.

This is where the cone differs fundamentally from adding more bars to the T.

Knowledge isn't really a set of isolated specialties connected by a thin line of general knowledge. As we learn, the spaces between those specialties begin to fill in. We see relationships. We recognize patterns. We understand how one part of a system affects another.

Our knowledge becomes increasingly integrated.

That idea is consistent with a broader body of thinking about professional development. David Epstein argues in Rangethat breadth of experience can be particularly valuable in complex and unpredictable environments.[2] Peter Senge's work on learning organizations and systems thinking similarly emphasizes understanding relationships and whole systems rather than viewing their components in isolation.[3]

Those ideas resonate strongly with my own experience. As my career progressed, my value increasingly came not from knowing one more isolated thing, but from understanding how the things I knew connected.

That is what the cone is intended to capture.

Depth, Mastery, and Curiosity

Even depth can be difficult to define. Early in a career, you may think your expertise is a particular technology or discipline. As you develop, you may discover that what you were learning was part of something much larger. For example, as your expertise in, say, Java or Python develops, you may discover that it is part of the broader discipline of programming, which is itself part of software engineering, architecture, and systems design, and so on. Like Russian nesting dolls, what once seemed like a complete domain of expertise becomes one component of something larger.

The Japanese concept of Shu-Ha-Ri[4] describes three stages of mastery: learning and following established practices (Shu), understanding and adapting them (Ha), and eventually transcending them through independent mastery (Ri). But each domain has its own progression. You might reach Ri in Java while still being at Shu in software architecture. You don't have to master one domain before exploring another, and your understanding of each can develop independently.

This is where curiosity becomes essential. Mastery in one domain doesn't automatically confer mastery in another. If we approach every unfamiliar discipline convinced that our existing expertise already gives us the answers, we stop asking questions. But if we remain curious about why things work the way they do, rather than assuming we already know, we continue discovering new layers of understanding.

Sometimes you have to go deep enough to discover what you are actually deep in.

There's Even Some Math

The engineer in me likes that the metaphor has a mathematical counterpart.

The volume of a cone is:

V = ⅓πr²h

The radius, r, can represent the breadth of your knowledge.

The height, h, can represent its depth.

And the volume represents the accumulated body of knowledge, experience, and perspective that you can bring to a problem.

This isn't intended as a literal equation for human capability. The equation describes the geometry of the metaphor, not the relative importance of breadth and depth.  You cannot plug someone's résumé into a formula and calculate their professional value.

But the geometry illustrates something useful.

Breadth and depth together determine the size and shape of the cone.

The next question is more interesting:

What determines how large that cone can become?

Intellect, Drive, and Longevity

I think three underlying factors have an enormous influence on the growth of the cone:

Intellect, Drive, and Longevity.

Intellect

People differ in their ability to absorb information, recognize patterns, work with abstractions, and understand complex systems.

We can improve our knowledge and develop better ways of thinking, but we don't get to choose all of our underlying cognitive abilities.

Intellect affects how readily we can turn experience into understanding.

But intellect by itself accomplishes surprisingly little.

A highly intelligent person who stops learning can build a remarkably small cone.

Drive

Drive is different.

Some of it may be dispositional. Some people seem naturally hungry to understand more, solve harder problems, or take on greater responsibility.

But drive can also be cultivated.

Purpose can strengthen it. Success can reinforce it. Good leaders can nurture it. An environment that gives people meaningful challenges can encourage it.

And curiosity may be one of its most important ingredients.

Curiosity makes you look beyond the assignment you were given.

Why does this software behave this way?

What happens to its output?

Who uses it next?

Why do they need it?

What problem are they trying to solve?

What happens if this fails?

Those questions are how my own cone expanded. I rarely sat down and decided, "Today I will broaden my professional knowledge."

I needed to solve a problem, and solving it well required understanding what was around it.

Then I wanted to know more.

Longevity

Finally, there is time.

Some things simply take years.

The popular idea that expertise requires “10,000 hours” comes from Malcolm Gladwell's Outliers, drawing on the work of psychologist K. Anders Ericsson and colleagues on deliberate practice.[5][6] The research is considerably more nuanced than a universal 10,000-hour rule: practice requirements vary substantially by domain, and practice is only one factor in developing expertise.[6]

But the underlying lesson remains useful:

Expertise takes time and sustained effort.

You cannot have twenty years of experience in five years.

But there is another side to that observation.

Twenty years passing does not necessarily give you twenty years of growth.

It can give you one year of growth repeated twenty times.

Time provides the opportunity.

What you do with it determines the result.

Time alone does not grow the cone. Time multiplied by curiosity does.

Put simply, Intellect influences what growth is possible, Drive influences how quickly growth occurs, and Longevity determines how long growth can continue.

What Shape Is Your Cone?

There is no ideal cone.

Your cone is constrained somewhat by the capabilities you bring with you. It is expanded by your drive. It is accumulated over time.

But its shape is largely yours to influence.

You can go deeper.

You can go wider.

You can deliberately move into unfamiliar territory.

And at different points in your career, you can change the direction in which you are growing.

And the cone doesn't necessarily have to be symmetrical. In geometry, an oblique cone has its apex offset from the center of its base. Professionally, I think of that as breadth that develops more strongly in particular directions. We don't learn everything around our core expertise equally. Our experiences, interests, opportunities, and choices pull us toward some adjacent areas more than others.

An engineer might develop tremendous breadth in technology and systems while having relatively little experience in finance or organizational leadership. Another might expand toward business strategy, management, and organizational development. Both are growing their cones, but in different directions.

For technical professionals, that choice becomes particularly important as careers advance. Staying at the absolute leading edge of a technical discipline takes enormous effort. So does developing the organizational, interpersonal, financial, strategic, and systems knowledge required for broader leadership.

There are only so many hours.

Growth therefore involves choices about where to invest them.

My own cone started with small pieces of software on a space telescope. Each problem led to another system, another discipline, another group of people, and another set of questions.

Decades later, the point is still there.

But the circle around it has become much larger.

And I hope it isn't finished growing.

So perhaps the question isn't whether you are an I-shaped or T-shaped professional.

Perhaps the better questions are:

What shape is your cone?

And is it the shape you want it to be?

References

[1] “T-shaped skills.” Wikipedia. The concept has a somewhat diffuse history: the term was reportedly used internally at McKinsey & Company in the 1980s, appeared in published discussions by the early 1990s and earlier, and was later popularized in design and interdisciplinary-team contexts by IDEO CEO Tim Brown. T-shaped skills overview

[2] Epstein, David. Range: Why Generalists Triumph in a Specialized World. Riverhead Books, 2019.

[3] Senge, Peter M. The Fifth Discipline: The Art & Practice of the Learning Organization. Doubleday, 1990.

[4] Wikipedia contributors. “Shuhari.” Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/wiki/Shuhari (accessed October 14, 2026).

[5] Gladwell, Malcolm. Outliers: The Story of Success. Little, Brown and Company, 2008.

[6] Ericsson, K. Anders, Ralf Th. Krampe, and Clemens Tesch-Römer. "The Role of Deliberate Practice in the Acquisition of Expert Performance." Psychological Review 100, no. 3 (1993): 363–406.

About the Author

Rob is the founder of Citadel Professional Solutions, where he helps professionals and organizations navigate career development, leadership, and complex business challenges. Drawing on decades of experience in software engineering, systems engineering, and leadership supporting the Hubble and James Webb Space Telescopes, he explores how technical expertise, organizational understanding, and leadership intersect.