Yes, I act opportunistically. It’s unreasonable not to. Maybe my willingness to pay for snacks is somewhere between the full price and half price. Maybe the idea of getting something for nothing induces a predictable irrationality in me. Now, if I could easily find out who lost their money to the machine, this would be a different story. Then I think I would have a moral obligation to return what’s not rightfully mine. But it’s infeasible to find this person. The welfare loss has already happened. There is no way for me to rectify the situation.

Somewhere, twice this semester, someone has been made worse off because of a vending machine. I had nothing to do with that. But once we accept that their loss is necessarily someone else’s gain, why shouldn’t it be mine? Is that really so terrible?