The one who hurts when you fail.
The one who focus your emotions towards one goal.
The one who redirect the pain toward the goal to become better.
He does not ask you to be the best, just a little better every single day.
This teacher is called curiosity, and most people lost it long ago.
If you already heard "Give a man a fish; you have fed him for today. Teach a man to fish, fed him forever."
I add : bring him back his child's curiosity and he will find a way to feed all his tribes for eternity.