(Is it that you can't do it or perhaps you don't want to do the work?)
When I was in college, I took a ton of advanced math courses, three or four of them, until one day I hit the wall. Too many dimensions, transformations and toroids for me to keep in my head. I was too stupid to do really hard math so I stopped.
Was it that I was too stupid, or did I merely decide that with my priorities, it wasn't worth the work?
Isn't it amazing that we'd rather call ourselves stupid than lazy? At least laziness is easy to fix.
People say that they are not gifted/talented/smart enough to play the trumpet/learn to code/write a book. That's crazy. Sure, it may be that they don't possess world-class talent, the sort of stuff that is one in a million. But too stupid to do something that millions and millions of people can do?
I'm not buying it. Call it as it is and live with it (or not). I'm just not willing to believe we're as stupid as we pretend to be.