The sunk cost fallacy is the tendency to continue doing something once an investment in resources like money, effort, or time has been made – even when it’s no longer rational to continue[xl]. In essence, it’s throwing good money after bad.
For instance, people who have bought a non-refundable movie ticket will still go see the movie despite not really wanting to (because otherwise they would “waste” the money spent for the ticket).
While in most cases the sunk cost fallacy leads to irrational decisions and even more waste, you can use it to your benefit to stay motivated to exercise – just pay upfront for a 3-month, 6-month, or 12-month pass at the gym (or elsewhere) and let yourself fall victim to the fallacy so you’ll have more motivation not to waste it.
I usually go swimming once a week. I don’t find it as enjoyable as other activities (though I still like it), so a 3-month pass (despite being extremely cheap) gives me additional motivation to visit the pool at least once a week. I don’t want to waste the money, even though skipping a few workouts would mean losing just a few bucks.
While this technique alone won’t guarantee you’ll stay motivated to exercise, it’s just another tool that will help you stick to your resolutions, hopefully for long enough to develop a permanent habit.