XP

In life it is very important to never get caught up on sunk costs. A sunk cost is basically any kind of expenditure that has already happened and you won't be recouping. One example of a sunk cost is a membership fee you've already paid.

If you've already paid for a month of gym membership, you will probably feel very obliged to use it. Maybe even to the point where you'd go to the gym instead of something such as riding your bike outdoors.

What's truly important is to look at a situation without bothering about any of your potential sunk costs. In the aforementioned scenario, the only question that should matter is if you want to go to the indoor gym or go outdoors biking.

When it comes to sunk costs, you should've already weighed your options before even incurring them. Even if you come to regret it, you still have to move on and look at the bigger picture.