I have found it is SUPER important to be mindful of this in life:

In economics, a sunk cost is any past cost that has already been paid and cannot be recovered. For example, a business may have invested a million dollars into new hardware. This money is now gone and cannot be recovered, so it shouldn’t figure into the business’s decision making process.

Or, let’s say you buy tickets to a concert. On the day of the event, you catch a cold. Even though you are sick, you decide to go to the concert because otherwise “you would have wasted your money”.

Boom! You just fell for the sunk cost fallacy.

Sure, you spent the money already. But you can’t get it back. If you aren’t going to have a good time at the concert, you only make your life worse by going.

They have a saying for this in poker: Don't throw good money after bad.