
There’s a good explanation as to why most of us stay in dead end relationships.
Why we continue to invest time, money and effort into people who have already gobbled a lion’s share of our lives.
Researchers believe it might be because of the “sunk cost effect”.
A “sunk cost” is a term generally applied in business or economics. It’s when a cost that has been incurred cannot be recovered.
Psychologists say the “sunk cost effect” occurs “when a prior investment in one option leads to a continuous investment in that option, despite not being the best decision.”

Think of it like this: you buy a ticket to see a film. Halfway through you realise the film is rubbish but you've already spent money on the ticket, invested time in going and devoted effort to the whole shebang.
It's unlikely you're going to walk out. Now try applying that principle to a shitty relationship.
Psychologists at the University of Minho in Portugal did just that and found individuals were more likely to stay in failing relationships if they had previously invested time, money and effort.
Two studies were conducted that presented individuals with hypothetical scenarios involving decision-making in relationships.

Top Comments
I read a good piece of advice recently:
Don't keep wasting your time on a mistake just because you spent a long time making it.
You could interchange 'time' here with money, energy, effort.