If I could give one piece of advice to any person in history, that advice would be...and why?

I would give advice to Adolf Hitler to probably tell him to kill himself if he doesn't stop persecuting the Jews. What he did was pure evil and extremely immoral. I'd tell him to stop or I'd personally take car of him myself without any hesitation or regret. I doubt he'd agree with what I'm telling him but I wouldn't except him to.