Rather than thinking of success as the source of happiness, we need to recognize that happiness is a source of success.
When you are happy, your brain simply works better. Happy people are more creative, solve problems faster, and tend to be more mentally alert. And more pleasant to be around.
Happiness is a choice. You can choose to be happy and positive. Even if it is not your default, you can totally retrain your brain to be more positive.
Start by consciously thinking happy thoughts, proactively looking on the bright side, and refocusing your brain when negative thoughts occur.
Your mind has the ability to determine how your brain thinks about what is going on in your life. Use it to your own advantage to reframe events and think positively.