More recently, other variables - in particular, personality traits and belief systems - have become of central interest in psychology. For example, Carol Dweck and her colleagues found that children who believed that they could improve their intelligence were better in task solving and more persistent when confronted with difficulty than children who thought their intelligence was fixed. Note that the two groups did not differ in their actual intelligence: all kids were matched on IQ.
http://www.psychologytoday.com/blog/mr-personality/201108/success-beyond-success-time-redefine-iq