Correcting past mistakes? By whose opinion were they mistakes?
Um...since in almost every episode the person's original choice led to them or someone close to them suffering a horrible tragedy, I'd say they qualify as mistakes to fix. For example, in one episode the guy he leaps into has to save a woman from a car crash that kills her. In another he's trying to prevent the guy's sister from marrying a dude who will beat her for the rest of her life. It's not like he leaps into people to prevent them from voting for Reagan in '80 or something.
I understand that. However, in real life, every action has a consequence. If a person dies in a car crash, then perhaps there are organs to be donated that would help save someone else's life. Now that other person will die.
The law of unintended consequences is huge in that show, and they just ignore it.