I remember learning about sunk costs in economics.. and how it applies to financial situations (such as your example in the restaraunt). In economics we would talk about in monetary term so I liked how you applied this to real life situations such as relationships!
One positive of the sunk cost fallacy can be the gym (we pay in advance) - so i could use the same attitude 'If already paid for it so midaswell use it :)
People fall for it in the gym, yes, and other classes: I paid for 10 classes/sessions. Even though I hate it, I'm going to make full use of them...
Yup. Most people dont take the positive angle for the gym but I think its a good way to look at it and use what you have paid for