Worst advice: "Don't try to make a carreer out of your passion"
The only professional I knew of as a kid repeated that lie when I, age 12, asked him for advice.
It was a meme from the 80's business 'genius' backwards-thinkers that I thankfully recognized as severely retarded. It took me 30 years to find out where he got that idea.
I learned at that moment that adults, the more credentialed they were, the more lies they would believe and spread around.