Those extra hours, it turned out, had been spent nailing down nitty-gritty details that only confused the students, and wound up getting cut from the lectures the next time Tom taught the class. The underlying issue, Tom eventually realized, was that he’d been using his own taste and judgment as a kind of proxy metric for his students’. This proxy metric worked reasonably well as an approximation, but it wasn’t worth overfitting—which explained why spending extra hours painstakingly “perfecting” all the slides had been counterproductive.
