Yesterday I attended a talk by Barry Rowan (former CFO of Nextel, acquired by Sprint in 2005 for $35Billion, and CEO of Vesper). The topic was about things he wish he had known early in his career. Basically, he talked about what makes he feel fulfilled.
He said that there are 3 keys to UNHAPPINESS: EXPECTING, COMPARING and COMPETING. As an example he said that in his 5 year Harvard Business School reunion, everyone was asking "how are you doing?". In reality they wanted to know about your professional position and even your salary. And it was not that they wanted to know your salary; they wanted to know how they were doing compared to others ("how am I doing?").
He also mentioned that "we can't get enough of what we don't really need". He quoted Rockefeller when he was asked "how much money is enough", and he replied, "just a little bit more".