They were praised for being "hard workers" meaning they could expect social approval for chugging through boring tasks. The first group already got their socia

They were praised for being "hard workers" meaning they could expect social approval for chugging through boring tasks. The first group already got their social approval for being smart. Once labeled "smart", they already "knew" they were smart. But ones that were labeled "hard workers" needed to keep up "hard work" to retain the (desired positive) label. Just compare: "I'm still smart, even if I performed bad on boring task." vs. "I'm still hard worker, even if I didn't put much effort into boring task."