I think we all have our views as to what makes us happy. In the sphere of religion, believers cannot understand how non believers can be happy when they have no after life to look forward to. Non believers cannot understand how believers can be happy when what they believe is so obviously false.
Philosophers and historians since way back have tried to generalize about universal notions which make people happy or give people some kind of hope. Some have said that in the U. S. the mystery and hope of “The Great Frontier” or “Western Movement” gave people optimism. There were historians who thought it gave men optimism and women misery. My wife in her book, Land in Her Own Name, debunked this latter theory.
Philosophers with a religious bent such as Aquinas are said to have been captured by a sense of wonder. It is understandable that if he found happiness in such wonder he would expect it to affect others in the same way.
I recall hearing a self improvement guy back in radio days who told of the need for everyone to have something they reach for that looks to be slightly beyond their current reach. For religious people that might be a life with sin resolved. To a non religious person it might be a better golf game or being completely absorbed in the fate of their favorite sports team.
Depression, in my unprofessional observation, strikes as many believers as non believers. Optimism and happiness seems the same.