Some excerpts from a good post on biases!
Being such a subconscious reaction, it’s hard to avoid this one. Our best bet is to try to separate the current facts we have from anything that happened in the past. For instance, if you buy a movie ticket only to realize the movie is terrible, you could either:
A) stay and watch the movie, to “get your money’s worth” since you’ve already paid for the ticket (sunk-cost fallacy)
B) leave the cinema and use that time to do something you’ll actually enjoy.
The thing to remember is this: You can’t get that investment back. It’s gone. Don’t let it cloud your judgment in whatever decision you’re making in this moment–let it remain in the past.