Numerous studies have shown that highly intelligent people may be more successful professionally. but, if they are happier than their less intelligent fellows, it is only very slightly.

This is counterintuitive. What could possibly account for this?

One explanation involves the difference in a person's ability to solve 'clearly defined' problems as opposed to being adept at solving 'loosely defined ' problems. 

Examples of clearly defined problems are math and chess problems.

Examples of loosely defined problems are 'What do I want to be, a dentist or a dancer?' or 'What should I do today?''

The people who are happiest are those most adept at solving 'loosely defined' problems.