Change happens. We don’t live long enough to observe most of it. It happens whether or not we want it or try to stop it. To accept the world as it is and learn how to adapt to it and learn to expect change, it seems, should lead to happiness. You can find data that shows the human to be a very adaptable animal that can learn to be happy in the most extreme conditions. What would make them unhappy? Change. The unfamiliarity introduced by extreme change induces stress that those who can make a game of it will enjoy, and those who see it as something to endure will suffer.