Happiness doesn't change as much as you think. In particular, your happiness is not as sensitive to what happens in your environment, as you might think it is. Umm.. Part of the reason for this is that there appears to be a strong inheritable basis for happiness. And some people talk in terms of the genetically determined set point. So you have a sort of natural happiness level, maybe a range. To put it in an extreme form, some people are genetically predisposed to be pretty sour, others to be pretty cheerful. What about life events? Wouldn't life events change your happiness? And here we are entering one of the great discoveries of happiness research. For many people, a very bad thing that could happen to you is to be paralysed from the neck down in an accident. It turns out, obviously common sense, that when this happens it makes them very unhappy. It makes them depressed, thinking their life is over, and they feel terribly sad. But not for that long. After about a year after being paralysed from the neck down, people's happiness comes back up pretty much to where it was before. Suggesting that there is a temporary effect, but not a permanent one.