> Well T-shaped individuals have greatest chance of success.

Personally, I feel like T-shaped individuals are a chimera. I don't know anyone whom I'd considered T-shaped. Maybe it's just my location. I have noticed that even the highest placed engineers at my companies, and I'm talking world leaders in certain areas, often do not like to venture even a little bit outside of their specialization.

> For example I am software developer so for business people I am a specialist. But I am also a "full stack developer" where for my fellow developers I am a generalist. Then I mostly specialize in .NET and Angular.

This I can absolutely agree with. I would not call that a T-shaped person; rather, to me, the above is a generalist. I do think that this depends on a point of view. But T-shaped person signifies that a person has one deep specialization. I'd say that having a deep specialization goes against going wide.

From my observation, I've never seen a person who'd have both deep specialization and be comfortable with other technologies on the side.

I specialize in .net too, but in a general way. i'm bad at everything. People who i work with who don't know anything about programming thinks i'm a specialist for some reason. luckily i'm the only programmer in my company. I feel like a fake, because I work for a really good company.

You're probably better than you think. If your company is good, it probably has a good culture and it feels there achieving great things requires not that much effort. I've felt that in good teams, big outcomes are easy, while bad teams will struggle to deliver simple projects. Also nowadays there are so many options to connect with other developers. Check the meetups (now most are virtual, so doesn't matter where you live much), or the indie hacker scene for example.

“I’m bad at a lot of things” - generalist

"I have a hammer, where are the nails?" - specialist

My friend's dad, the handyman, always said:

"I may not be fast, but at least I'm not good."

As with most categories, labels, and taxonomy, the dichotomy is a human construct. Of course it's not true absolutely. But it still has utility to ponder, and when applied to specific contexts can be powerful.

It's not at all clear to me why a T-shaped individual would be better than "square" individual of the same depth (ie something with more overall surface area).

I'd say the assumption is that your square shape would sacrifice breadth for depth across their breadth. The assumption is that time is fixed and you can only learn and master a certain amount of material to a certain degree. At some point you're going to sacrifice something for the other because time is fixed. There's probably another element to consider: memory, learning rate, and rate of change of a given industry. If an industry moves fast your dabbling in that field can useless fairly quickly.

The assumption that somebody needs to have sacrificed breadth for depth is only true in the hypothetical case where you need to choose between two applicants with exactly the same amount of experience. In practice, you will encounter candidates who are just better at everything than the other candidate. That is something experience can give you.