The sunk cost fallacy

So, I've been teaching economics.  This is a bit funny because I hated economics in college and skipped it more than any other class (except maybe that one physics class).  It didn't help that the class was something like 1000 people taught in that auditorium building on the quad.  The memories are hazy, the subject never made sense to me, and I still can't properly draw a supply and demand curve.  None-the-less, a group of engineering students are being subjected to my explanations of how economics applies to engineering on a weekly basis.  Because I have a PhD - that's why.

This has not been a good semester to be teaching a new class.  Conferences, search committees, death.... let's just say I bored MYSELF in class last night because I haven't had the time to prepare as much as I'd like to.  But in light of the challenging year, I've been thinking more about something I talk about in the economics class - Sunk Costs.

Sunk Costs (for anyone who remembers as much of their college economics classes as I do) are those expenses in the past.  No matter what the present circumstance, you cannot change the past costs.  They are paid.  End of Story.  Your best move is to consider the current circumstances and make the best decisions regarding the future.

Simple.

Except it's not.

Have you ever eaten the food on your plate because otherwise it would go to waste, only to end up feeling slightly ill after the meal and your feelings about the experience significantly lower than they would have been if you would have just quit eating when you were full?  (sunk costs)  Have you ever held onto a pair of pants that you've never worn because there is something wrong with them that you didn't realize until you brought them home and now you can't take them back but every time you look at them hanging in the closet you are reminded that you spent money on something you've never used?  (sunk costs)

So - why am I hanging on to "stuff" that I don't use, probably won't use, and if I ever do decide to use will be obsolete?  Wouldn't I be happier with less stuff to see, clean, and move around the house in laundry baskets masquerading as boxes?  Why do we continue to do therapy with Allison, even though we don't think it's going well?  Because we've invested so much time in it.  Does that invested time make the the next session go better?  No.  "You can't quit piano, you've done it for 5 years."  So what? - if you aren't going to enjoy the next year, could your time be better spent elsewhere?  And Candy Crush - need I say more?

We value a certain amount of stick-to-it-ivness.  And I don't think that's bad if the end payoff will be positive.  Yes, keep the backpacking equipment that you haven't used for 4 years if you anticipate using it for an awesome trip in a few years when the kids are older.  But if you don't like rollerblading - don't hang on to them just because they were expensive in the first place.