Zack Wehrwein at Current Affairs reviews Grit:
"Social scientists typically refer to this bias as “sampling on the dependent variable.” That is to say, her dependent variable of interest, the thing she wishes to explain, is achievement, and she only selects cases with high achieving individuals. One might be impressed to learn that 98% of “gritty” West Point cadets made it through Beast Barracks, but there’s an additional statistic you need to know: 95% of all West point cadets make it through. ... Thus grit may explain something, but it doesn’t explain much. It might tell us why certain West Point cadets do slightly better than certain other West Point cadets. But it leaves aside an important question: how do people become West Point cadets to begin with?
In fact, we don’t even know that “grit” at West Point tells us anything about success at all. That’s because Duckworth doesn’t study the people who leave West Point, just the people who stay. But for all we know, the people who drop out are not failures. Perhaps they just didn’t enjoy military service that much. Is it really that unthinkable that a few of the more independent-minded 18 year olds could arrive at West Point, only to make a swift exit after having a drill instructor scream in their face because a quarter didn’t bounce off the bed? It could be that plenty of (eventually highly successful) people come in with a naïve, romantic notion of military service, but quickly figure out it’s not for them. Duckworth hasn’t produced a study showing that grit predicts success, but one showing that grit predicts conformity and the ability to endure institutions. ...
Duckworth has given the misleading impression that grit is what’s needed to overcome structural obstacles, even though she has only studied the people who have made it past those structural obstacles already."