The third force that keeps people from quitting is a tendency to focus on concrete costs and pay too
little attention to opportunity cost. This is the notion that for every dollar or hour or brain cell you
spend on one thing, you surrender the opportunity to spend it elsewhere. Concrete costs are usually
easy to calculate, but opportunity cost is harder. If you want to go back to school to get an MBA, you
know it’ll cost two years’ time and $80,000—but what might you have done with that time and money
had you not been in school? Or let’s say you’ve been a competitive runner for years and it’s still a big
part of your identity—but what else might you accomplish if you weren’t slamming your joints into
the pavement twenty hours a week? Might you do something that makes your life, or others’ lives,
more fulfilling, more productive, more exciting? Perhaps. If only you weren’t so worried about the
sunk costs. If only you could quit.