"What the secret to a happy life?"
I think you should love yourself before you can be happy in life. You start to feel confident when you surround yourself with people and things that make you happy. To feel happy, you have to ignore the people who try to bring you down. Also, by saying positive thoughts about yourself eventually will trick your brain to believe anything you say to yourself. Another thing is to not overthink too much. “If it's not going to matter in five years then it doesn’t matter.” Lastly, don’t push yourself to the point where you feel overwhelmed, and find something else that makes you happy.