Inverse Utility Monster: deliberately goes through hell, returns superpowered.

Vegeta from Dragon Ball once deliberately had himself beat to near-death for that very reason.

Inverse Utility Monster: deliberately goes through hell, returns superpowered.

Specifically:

Sign up for the Auror preparation program in your sixth year. It's the next best thing. Oh, and if a famous Auror offers to oversee your summer internship, just ignore anyone who warns you that he's a terrible influence or that you're almost certainly going to die.