Happiness and success? Knowing who you are. Many people, when asked about themselves, start with saying, “I work for X company.” Then, if faced with a sudden job loss or company closure, they must determine how to define themselves independently of work. Many, if not most, will find themselves in this situation at some point.
If you are comfortable with who you are, have confidence in yourself, and don’t depend on your self-image coming from your job, I think you’ll be happy.