Everybody wishes they could time-travel back and tell their younger self something. Tell your current self; it’s cheaper.

The advice people imagine giving their younger selves is almost never new information. It is usually something they already half knew and did not act on: stop worrying what they think, call her, start now. If it was available back then, some version of it is available today, addressed to you.

Write down what you would tell fifteen-year-old you. Read it back as though it arrived from somebody ten years ahead of where you are standing. Most of the time it still applies word for word, and the only new part is whether you do anything with it.