Surround yourself with people who challenge you, not just those who agree with you.

The greatest obstacle to being heroic is the doubt whether one may not be going to prove one's self a fool; the truest heroism is to resist the doubt, and the profoundest wisdom to know when it ought to be resisted, and when it be obeyed.

Don’t fear failure. — Not failure, but low aim, is the crime. In great attempts it is glorious even to fail.