1. Those who believe that intelligence is fixed from birth, and
2. Those who believe that intelligence can be improved
The finding was that folks in category (1) tended to be fearful of being wrong, and had trouble succeeding in life whereas the folks in category (2) felt it was OK or good to make mistakes, and tended to be more successful.
EDIT: article is http://www.nytimes.com/2008/07/06/business/06unbox.html