Charlie Munger (co-founder of Berkshire Hathaway) talked a lot about Circle of Competence. Here is one of his quotes:
You have to figure out what your own aptitudes are. If you play games where other people have the aptitudes and you don’t, you’re going to lose. And that’s as close to certain as any prediction that you can make. You have to figure out where you’ve got an edge. And you’ve got to play within your own circle of competence.
I love this quote as it’s a compelling way to reflect on your strengths and draw a perimeter around your limits. But while "Circle of Competence" is great for knowing your boundaries, it is not really useful for growing your expertise. That got me thinking: what mental model actually helps you grow in your field?
To be an expert in an area, some folks argue that you should have T shaped knowledge (or π shaped knowledge). T shaped knowledge is a conceptualisation of how to be an expert at one thing. The stem of the T denotes your expertise and the horizontal line on top of the stem represents little bits of knowledge about other related things to that expertise.
I like the framing of "T shaped Knowledge" and find it somewhat useful but i think it is insufficient for how to be an expert in a particular area.
So what model is useful AND sufficient to be an expert? It dawned on me one day that an answer to this is to think about expertise as a wheel with spokes. That is, instead of modelling your growth as T shaped or Pi shaped knowledge, one could just extend Charlie Munger's Circle of Competence in a 3 dimensional format.
Imagine that the area you're interested in is like a bicycle wheel with spokes. Each facet of this interest area represents a spoke.
For example, in the wheel of Product Design, Figma (a design software tool) can be a spoke, photoshop can be another spoke, behaviourial psychology can also be a spoke.
An expert in the area of Product Design will have many spokes on his/her wheel.
The more spokes that are on your wheel, the more you know. In addition, the more you know about a particular facet the thicker the spoke. So you can have a variation of thickness on the different spokes on the wheel.
One of the most valuable aspects of this model is how it’s prompted me to reflect on questions such as:
To continue in the same vein you can also ask: What other wheels connect to this wheel and what are the spokes in that wheel?
So to conclude, this model is useful as it can help round up all the different aspects of the area you're interested in. Plus it is sufficient as you can keep adding spokes to the wheel.