After much introspection, I think I have identified the most critical personality trait to a successful and happy entrepreneur.
You have to be positive.
You need to be a glass is not just half-full, you have to see even the smallest amount in your cup as fantastic and that it will get fuller and runneth over. Without this every other quality we think of for entrepreneurs: thick skin, persistent, ambitious, leaders, surrounding themselves with terrific people / team building, among others.
Being positive isn’t always possible. You are born with it or those with depression, BP2, dysthymia, addictive personalities can control it and adopt these qualities. But a positive outlook is critical. My favorite example of a CEO with this quality is Warren Buffett. If your thought is, of course, he is happy is one of the richest people in the world (and without his generosity, he would likely have held the top spot more years since his giving pledge). His motivation is not to accumulate wealth and be ranked #1 on a Forbes list. He has done so well as an investor and business leader by always believing the U.S. economy and people will always improve and have a higher quality of life in the long-term. He has attracted businesses and deals no one else could get because of this outlook and demeanor.
If you are not able to be in this mindset, reconsider being an entrepreneur until you can get this outlook. As I finally acquiesce and acknowledge my own failures as an entrepreneur, friend, and partner — this is the single most important thing I need to improve.