Ambitions, e.g. for success at work or sport, are natural and come from the urge to have a high social ranking. After all we're first and foremost social beings. So our position among others is inherently important to us. But we're not living in clans any more. Civilisation has made things difficult. This kind of success (to assert ourselves over others) is overly glorified. Athletes are looked at god-like. Money and fame are overrated. To some extend it's natural to try to be successful, but the world is full of extremely successful people who find themselves being unhappy.

Those people often see that helping others is a true source of happiness.

Matthieu Ricard is a quite famous monk having published a lot of interesting stuff:

http://www.matthieuricard.org/en/

This one is on the topic:

http://www.matthieuricard.org/en/books/happiness-a-guide-to-...