I absolutely believe that there's nothing I cannot do, given the time and energy. I've run 2 marathons at the point of mental fatigue. I've cut as many as 20 lbs in a week for wrestling. I finished a college degree with honors while getting at least a dozen confirmed concussions, who knows how many unconfirmed, and while still competing.
I really feel like I can conquer anything. I actually gave up NCAA to work for free at as many startups I could during my 4th year to do the jobs that no one wanted to do. I definitely feel like a made the right decision. I can't be a pro wrestler these days :)
Edit: Typos -- the head bonks are showing :)