When Emily Anderson first taught economics at Blaine High School, she also worked weekends at a busy restaurant/bar. She made good money, so she put in as many hours as she could. She rarely saw her friends, and she and her husband skipped their honeymoon.

One day in class she was explaining the concept of "opportunity cost" — which she defines as "what you lose when you choose; the value of the alternative given up when you make a choice."

"I remember an 'ah-ha' moment," she says, "when I realized that while most people probably don't think enough about opportunity cost, I had been so focused on [the job] that I had missed out on many great things in life."

That lesson resonated with her students, and with her. She gave up the weekend job.