Teach a younger kid the thing you wish someone had taught you. That’s how you get to be in two timelines at once.

Knowledge you had to work out alone is usually the knowledge you can explain best, because you still remember precisely where it was confusing. Handing it down saves somebody the detour and leaves a piece of you somewhere you will never be. They keep using it long after forgetting who showed them.

Name one thing you figured out the hard way and find somebody two or three years behind you. Show them once, plainly, without letting it become a lecture. Ten minutes of your time can delete a year of theirs.