People should learn how to be happy no matter their situation. Although there can always be extenuating circumstances in general being happy should be a rule of thumb. If you are not happy how you are supposed to succeed at anything you want to do in life. There are many versions of life. I do not believe that people necessarily start off good or evil. I think we learn from our environments, learn from the people around us and put ourselves into dire situations when necessity calls. Sometimes, those dire situations bring us where we never thought we would be.
A person could be successful and still be a rotten human being. This could come from anger, sadness, depression or any other number of internal triggers. I do not know about you, but if I am going to be successful I want to be happy at the same time. Now this is where the choice to be happy can come into play. Think about the life you want. Being happy has been proven to keep the body healthier and the people around people who are happy are happier.
If you can choose to be happy no matter what your circumstances are right now success has no choice but to follow. You can succeed in relationships. You can succeed in work. You can succeed in finances. Most of all you can succeed in life.