Everyone is different. However, I think people can be happy if they choose to be. There are people who have gone through a lot of things and are still happy because they choose not to let bad things affect the way they feel. I don't think people really stumble upon happiness because you can't wait for things to happen in your favor, you have to go out and make things happen.
Credit goes to eeveelover824 for the team pose and SM for the userbar