Sometimes a logical fallacy isn’t a fallacy when you’re talking about human interactions

The “sunk cost fallacy” (explanation here) is often held up as one way that normally rational people fall prey to silly, silly irrationality.   And along those same lines, I’ve seen a number of folks try to apply this metric to relationships.

In pure economics, a sunk cost is when you’ve already spent money that you can’t get back.  A classic example is continuing to invest in a crappy company so you don’t “lose” the cash you’ve already invested.

But that isn’t how relationships work.1

If you try to avoid this “fallacy” in economics, you’ll stop investing in a company when things go south.   To quote Wikipedia:

Traditional economics proposes that economic actors should not let sunk costs influence their decisions. Doing so would not be rationally assessing a decision exclusively on its own merits.

And that makes sense when you’re talking about economics.

But it’s complete and utter bullshit when you’re talking about people.

Obligatory disclaimer time:  Just because you’ve been in a relationship a long time does not inherently give it value.  Especially if there’s a recurring pattern of problematic behavior.


In a typical relationship, there’s going to be tough times.  There may even be horrible times.  It doesn’t matter why that is – perhaps one partner lost a job, perhaps there’s a chemical imbalance that got out of hand, perhaps someone got ill, perhaps there’s a stressor that completely freaked out someone.

In those cases, when there’s not a consistent, ongoing pattern of problematic behavior, the sunk cost fallacy saves relationships.

Try this on for size:  You are with a partner because they’re… well, for lack of a better word, fun.  It’s good to be around them.

And then they get sick.  Like, seriously sick.

And they’re not fun anymore.

Traditional economics – or some pure rationalism bullcrap – would have you dropping that partner like a hot stone.  After all, they’re not making your life better right now.

Which is a hugely sociopathic and selfish way to behave.

The sunk-cost fallacy fails when it comes to most relationships because sometimes there’s really, really rough spots.  It’s not merely an averaging out of how things are going in the relationship;  it’s knowing how good things can be.

Armed with that knowledge, it’s possible to then address the rough patches as rough patches instead of some kind of traumatic disruption.

Yes, the cardinal rule of relationships applies.  Without that cardinal rule, you should DTMFA.

But a rough patch – even a massive disruption in the relationship – doesn’t mean you should suddenly ignore everything that came before.

1 Nevermind that the idea of quantifying the value of relationships by what you gain by them is abhorrent to begin with. Just stick with me here.