I think you become great by accident, as a side effect of solving difficult problems with great tenaciousness and energy.
One risk with doing things in isolation is hitting a local maxima. That is, getting really good using an approach that will only get you so far before super-human effort is required. For example, mastering VB 6.
It really helps when there are others who have gone ahead and made assorted mistakes to tell you when you may be following a poor path.
If you want to become better, but do not find yourself periodically challenged (or at least stretched a little), look for additional opportunities to do so.
I'm sure the Dunning-Kruger effect comes into play here.
http://rationalwiki.org/wiki/Dunning-Kruger_effect
Thinking you're great before you are, in fact, great, will surely hold you back.