The human brain is a powerful and bizarre thing with biases that cause us to make bad decisions. Of those, there's one in particular that we apply to relationships. Have you ever been in a relationship when you knew that deep down, it wasn't working but you didn't want to end it, because of how long you were in the relationship? There's actually a term for that: the sunk cost fallacy.

The sunk cost fallacy is traditionally applied to matters of economics and business, but that's changing. Sunk cost fallacy is the new buzzword on the internet (particularly the Reddit relationships community) and among psychologists when doling out relationship advice.

A sunk cost is a cost you've acquired that you can't recoup. In business, this cost is money. If you sink all of your money into a house that turns out to be a bad investment — like it's built on a shoddy foundation, the location winds up being a nightmare, it's haunted, whatever — you're reluctant to give it up because of how much money you put into it to make it livable.

But the truth is, it isn't livable, and the longer you stay in the house, the more you're basically screwing yourself. Now apply this to relationships, but swap "money" for "time."

Lifehacker wrote a piece about how the sunk fallacy cost makes you act stupid, and they use staying in a bad relationship as an example of this in action. You tell yourself, I've spent so much time with this person investing in this relationship, so how can I just leave? "This is unfortunately all too common," Lifehacker reports.

NPR devoted an entire segment to the sunk cost fallacy and how it applies to love. They spoke with 30-something Megan McArdle, who told her tale of heartbreak. She spent years with a man believing they would wind up getting married, despite evidence her partner was showing that they were not on the same page. McArdle didn't want to leave the relationship, because she had "invested" so much into it.

Funnily enough, McArdle's day job was writing about economics, and it was her trade that led her to realize she was staying in the relationship because of the sunk cost fallacy.

"And that's exactly what I was doing over and over and over again," McArdle explains. "I just couldn't let go and say, you know what? I invested all this time, and he's great but this relationship is not going anywhere and I have to let it go and go look for one that is."

Psychologist Robin S. Haight commented on this alarming rationalization towards relationships, and notes that what it comes down to is "avoidance."

"[It's] an avoidance of disappointment or loss when something doesn’t work out. When a relationship doesn’t succeed, especially after a long period, especially after many shared experiences and especially after developing a hope that the relationship would be a good one, it is a loss. [...] Another angle to evaluate is that focus on 'sunk cost' creates a distraction from one’s inner truth. The sentence often goes like, 'I’ve already invested to much, so I can’t notice my thoughts and feelings that are telling me to end or change this relationship.' This is a type of insidious defense against noticing yourself."

Another reason why people stay in relationships is because they feel they're stuck in an endless loop of unhappiness and don't think they can get out. "I think that all of these situations start out with the potential cycle-breaker feeling flattered by the attention and promises of change, but the reality is that these kinds of manipulators — or even 'abusers,' if you will — don’t change, but their partners have to," says relationship counselor Bonnie Kaye, M.Ed. "The cycle-breaker needs to set boundaries quickly before getting sucked in again and again."

And that's why it's so temping to stay in a toxic relationship even if you know it isn't good for you. But to quote Dr. Phil, "The only thing worse than being in a bad relationship for a year is being in a bad relationship for a year and one day."