“A group of fifth grade students are individually given a puzzle to solve. Some of the students who solve the puzzle are praised for being smart; other students who solve it are praised for having worked hard. The students are then invited to choose another puzzle: either one of similar difficulty or one that’s harder but that they would learn from by making the effort to try solving. A majority of the students who are praised for their smarts pick the easier puzzle; 90 percent of the kids praised for effort pick the harder one.”