Tough question.
It is. I been thinking about it for a few days already. It's thought in progress.
I can think of a few things I could tell myself but that's simple things like watch what I eat, never buy a Limp Bizkit CD, save my money, don't go to Plainview on a random summer saturday night, avoid that smoking phase and so on.
These things above are cool and all but not sure they're significant in terms of life-altering or world-altering. Maybe I would tell myself, "To make sure I see PanterA before Dimebag gets his brains blown out by some psycho with no permission. " This or preventing the murder all together could change the world plays out it's life. I could become president!
I need to think about this more.