Stuff I learned in design school (that they never taught me)

Enemies can be unwittingly helpful
So someone hates you and is being turdy to you, trying to tear you down in front of the class, and your lecturers, in the hope of getting better grades. That doesn't mean you don't listen to them closely and analyse what they've said. Sometimes a grain of truth in it that helps you, even if it burrrrns it burrrrrns. Learning to find those grains of truth is a skill in and of itself.

Someone being better at something than you are, doesn't make you any less good at it
However, it still makes you less desirable in the job market, should you be in direct competition with one another.

Serve your client, not your ego
You may love sword and sorcery, but that doesn't mean you put sword and sorcery into every freaking thing you do. Especially not stuff that has nothing at all to do with it, and whose target market thinks the whole S&S thing is utterly stupid.

Keep your principles, change your designs
Almost, but not quite, the same as the above about serving your client.

...and of course, there's the last thing I only learned when I went out to work.

Sometimes people pay you for the privilege of overriding your professional advice
If you fail to convince them after doing your best to make them understand, and if you leave paper trails (when needed), you've earned the money.