To paraphrase the well-known prayer (the original: Lord, give me the courage to change that which can be changed, the serenity to accept that which cannot be changed, and the wisdom to tell the difference): May I have the courage to say "no" to those things I shouldn't do, the grit to stick with those I should do, and the wisdom to tell the difference.

Saying "no" is a critical skill. But having the grit to stick with the things you shouldn't quit is the best predictor of success.