The devil is the reason you felt pain during your training, If you felt no pain, You didn't even have a reason to train and ended up breaking your body without knowing when to stop, Therefor, The devil helped you realize your limits and how to overcome them, The pain of giving up and becoming a loser is even worse, Therefor the devil taught you when you start, You can't stop. Forcing you to train endlessly.
Therefor, The devil made you do it.

I should probably lay off the mushrooms.