Write the lesson down while it still stings. Memory smooths the edges and loses the point.

The sharp version is the accurate one. Within a week the memory rounds off, the specifics fade, and what is left is a general impression far too comfortable to act on. That smoothing is protective, and it costs you exactly the detail you would need in order to avoid repeating the thing.

Write it down within a day, while you still remember what it felt like and where precisely it went wrong. Keep it short and concrete. Reading your own words from that moment later is more persuasive than any advice, because it came from somebody with nothing to sell you.