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I paid 24 euros for a six-hundred-page essay and got to page two hundred and twelve, having known since page sixty that it was giving me nothing. I kept going because I had already paid for it.
That has had a name since 1985. The psychologists Hal Arkes and Catherine Blumer handed out season tickets to a university theatre at randomly assigned discounts: the people who had paid full price attended more performances over the following months, even though the plays were exactly the same. Money spent never comes back, but it weighs.
With books the real cost isn't measured in those 24 euros, it's measured in nights. Four nights on that essay are four nights I didn't give to another book.
So now I do something silly that works: when I hesitate, I write down the page and give it fifty more. If I'm still hesitating at page fifty-one, I close it and move it to the bottom shelf.