“Erfahrung heißt gar nichts. Man kann seine Sache auch 35 Jahre lang schlecht machen.” - Kurt Tucholsky
Which DeepL translates to
“Experience means nothing. You can do a bad job for 35 years.”
Not strictly life changing, but a very valuable reminder, if you need to deal with ‘that’ kind of person.
This. Always be kind to your future self.