An early mistake can be useful when you remember where and why it happened.

Mistakes are only educational when the circumstances survive them. Remembering that something went wrong tells you almost nothing; remembering that you were rushing, that the instructions were ambiguous, or that you skipped a check because it seemed unnecessary tells you what to change. Otherwise the same conditions reappear, produce the same result, and it feels like bad luck.

After something goes wrong, write two lines the same day: what happened, and what the situation around it was. Include the pressure you were under. Read the note when you next meet those conditions, because you will not recognise them otherwise.