It doesn't really matter how good you are at something, if you do that thing in isolation without feedback from peers or an audience, you'll quickly stagnate.
I'm seeing more and more clearly that my career progression has continued to stall by being in a team of one far too many times. Difficult tasks scare me, familiar tasks are comforting, and I'm always sure that my work sucks.
Constructive criticism to improve, praise to confirm ability.