You’ve heard this trick before: If you want to eat less, just use smaller plates. Pretty clever, and most of the time it seems to work. But there’s a catch. A new study in Appetite found that the small-plate rule doesn’t work unless you have some really good self-discipline. Basically, the study found that if you’re really hungry, the size of the plate doesn’t matter. You’re going to overeat no matter what. Keep that in mind during your next potluck. And don’t go back for seconds.