A few things I learned from Economics in college that have ended up being generally applicable in life and at work.
1. Opportunity Cost: The cost of something is what you don't get to do as an alternative. If I stay late at work, I miss dinner with my family.
2. Sunk Cost Fallacy: Don't stick with something just because you've put time, effort or money into it. Evaluate continuing against simply doing something else. If I start a new Netflix series that sucks, I don't have to finish it.