I realize that this isn't really a big revelation, but it didn't really hit home for me until I got into a real "career" -- it wasn't such a big deal when I worked retail jobs.
but seriously, probably thinking i had to "pay my dues" before I begun my career. Thinking I wasn't good enough to get a job, and I had to spend time at Uni first. It wasn't until I was mid way through my masters before I realised that a job wasn't going to magically appear the day I graduated. I dropped out and never looked back.
Also, thinking I had to shoehorn myself into the industry by working my way up to it from tech support. That was fruitless.
They do the same for most math. Always learned math better when it was being applied to actual things I cared about personally.
Nearly drowned in toxic work culture..