A lot of emphasizes is been placed on academic excellence as the major measure of intelligence. But there are also other forms like emotional intelligence. And it is a great deal in how successful someone will become.

It is not only how much you know but how much you apply whatever you know which entails your character, guts, confidence, relentlessness, relationships with others and stuffs like that.
All these are likely to be taken for granted by the brilliant students, they know how intelligent they are and are more likely to overly dependent on their intelligence and neglect others things that matter.