The One With the Sunk Cost

We've been on the topic of fallacies lately and I owe my esteemed co-blogger SK a thank-you for educating me about them, so I thought I'd offer one. I look forward to your thoughts. (I'll also borrow SK's disclaimer that thought experiments are included in this post, and if you dislike Friends you may want to stop reading now. Are there people who dislike Friends ?) This fallacy is a favorite of mine: "sunk cost." Logically Fallacious offers a nice definition and examples, but basically I think of it as, "This [project/relationship/activity] isn't working and doesn't seem likely to get better, but I can't walk away because I've already put so much [effort/time/money] into it!" As an example, I like to ask people whether they finish a book or movie they're not enjoying. If they tell me they stick with it to the bitter end, I'm always curious about their reasoning. Because they've already spent time on i