Margen
Sunk cost is simple to say and hard to apply: the money or time already gone won't come back, so it doesn't count in the decision you make now. A small experiment makes it visible. In 1985, Arkes and Blumer, two psychologists at Ohio University, sold season tickets to a local theatre. A third of the buyers paid full price (15 dollars). A third got a 47 % discount. The last third paid nothing. Then they counted how many plays each group actually attended. The discount and free groups went to fewer plays than the ones who had paid full price. The only difference was in their heads: those who paid more felt they had to make the most of it.
Three steps to avoid the same trap:
1. Write in one line what you still have to spend (money, time, energy) if you keep going.
2. Ask the future this question: «If they were offering it to me for the first time today, at this price and knowing what I now know, would I take it?».
3. If the answer is no, you stop. The money already spent isn't saved by carrying on: it's lost twice.
Good for gyms you don't set foot in, series with nine seasons, courses begun in March, and projects nobody is excited about any more.