Author is probably referring to the study that kids who are praised on being "smart" do less well than kids who are praised on being "hard working".
Here's the first google result, looks like it:
http://www.scientificamerican.com/article.cfm?id=the-secret-...
Jives true to me as well. Most of the people who have identities based on being smart far underperform their intelligence. I was praised for being smart growing up, I fight that off like crazy now. "Me? Not smart at all. Just curious." "Nah, I'm dumb as a box of rocks. I just keep going." And so on. It's done wonders for me. (Also, realizing just how much I didn't know was pretty humbling - and the scariest is realizing how much that I'm not even aware I don't know...)