Sunk cost

One hard rule in business is to ignore sunk cost. Sunk cost refers to the money that has previously been invested into a project that has no hope for a positive outcome. This idea has also been called the Concorde fallacy. For almost 30 years, the British and French government poured millions of dollars into the Concorde jet even though there was no ability for the airliner to make a profit. 

Sunk cost often leads us to make poor decisions. It's hard for a person to walk away from a poker game with $20 invested, but even harder for the guy with $100 in the game. People often will sit through a horrible movie just because they paid for the ticket. Just because you bought a terrible book, doesn't mean you need to spend 8 more hours finishing it. 

Likewise, some people stay in their current job because of the 10 years of experience and don't want to waste that investment.

There might be areas in your life that you have spent time or money that are not worth further investment. Try to see where you might have sunk cost in your life. Don't make future decisions based on sunk cost.