“Whatever doesn’t kill you makes you stranger” is probably the shallowest of all overly praised movie quotes of all time.
It’s a nothing burger. A non-thought. A loud pop of an empty cracker that workers forgot to fill with confetti and a toy back at the factory. It’s complete purpose is to put something pretty in the mouth of Joker to have people say on repeat with a fake satisfaction of having shared something deep.

It’s NOT.