The young athlete who aspires to greatness, generally speaking, learns a number of things from several different coaches. The first one taught him the fundamentals; the second one instilled discipline in him and taught him more of the techniques that must be mastered to excel.
You may not be able to change the world, but when you change your world, you have taken a major step in changing the world. And when you change your world for the better, you have positioned yourself perfectly to change the world of those around you.
If you can dream it, you can achieve it.
Yes, it's absolutely true that anything worth doing is worth doing poorly - until you can learn to do it well.