From: Gayle Laakmann McDowell, Consultant (tech hiring/interviewing), Author (Cracking the * Interview), Coder
“Don’t mix business with pleasure” is saying that you shouldn’t become friends or date people at the office. The idea (which I don’t particularly agree with) is that it will complicate your office life and your personal life, leading to conflicts in both.
“Make passion your profession” is saying that your career should be whatever you’re most passionate about.
There is wisdom to both expressions, but they are also problematic.
It is important that you enjoy your job (if at all possible), but this doesn’t mean that your career should be the thing you’re most passionate about. Your ability to support yourself and your family matters too. Not being able to do so could quickly sour yourself on your passion.
Similarly, being friends with your coworkers can add complications, but it also makes your job more enjoyable. If you tend to have drama-filled friendships, maybe you should stay strictly professional. Otherwise, having work friendships is probably a good thing.