I'm happy to see some of the examples here are of bad advice.

The worst, specific piece of advice I received was when I was choosing a major in my senior year of HS, which informed where I went to college. For some paths like engineering you need to know before you matriculate at some schools.

The bad advice which was handed out in 2001, was that CS as a career had peaked and all those jobs created during the dotcom boom would be outsourced, so there was no point in majoring in it anymore.

I unfortunately took that advice for a few years, before realizing it was bunk and having to spend extra time in school to enter a career in software.