My name is Sam Vaknin, and I am the author of Malignant Self-Love, Narcissism Revisited.

The tendency to remain in bad relationships, the tendency to stick to partners who are abusive, in hopeless, sexless, loveless, doomed marriages and other unions. This tendency is known as the sunk-cost bias or sunk-cost fallacy or the concord fallacy.

Co-owning a business or property, shared memories and especially co-parenting tend to cement this bias and pile it on top of traumatic bonding and fused relationships.

What is the sunk cost fallacy or bias?

Well, in day-to-day life, we tend to throw good money after bad just because we are already invested in a project or in a stock. We watch an atrocious movie to its end because we have already spent an hour doing exactly the same. We eat food that we have ordered even if it sucks. We keep clothes that we never wear simply because we have paid for them.

It is a particularly pernicious brand of loss aversion, the proclivity to avoid waste. This utterly irrational behavior is motivated by malignant optimism, an over-estimation of the probabilities of positive outcomes if we just keep going or keep doing something differently.

Someone said that the definition of insanity is doing the same thing, expecting different outcomes and that is a pretty good definition of the sunk-cost bias.

We are also afraid to look foolish if we admit to having made the wrong decisions consistently. This is a form of narcissistic injury.

We sometimes feel responsible and guilty for having made these decisions in the first place, so we atone for our mistakes.

Of course, the rational thing to do is to cut your losses and abandon the dysfunctional relationship, but divorce statistics aside, surprisingly few people do so in time.

What are the results? What are the outcomes of this reluctance?

Wrecked marriages, hateful exes, bruised children and crumbling enterprises.

The sunk-cost fallacy or bias ends up sinking the people who are perpetrated.