I learned through hard lessons, that when I want what I need, I get what I want.
There is actually a suggested answer, called Maslow's "Hierarchy of Needs".
Psychologist Abraham Maslow has suggested, if I understand it, that human beings have a constant urge to improve themselves. He imagined a pyramid. At the bottom are basic needs like food and shelter. If we don't have those, we focus on them, and can't think of anything else except survival. But if we do get them, instead of being satisfied, we move up a level and focus on something more sophisticated. And so on.
It can sound like never being happy, but is also a process of trying to be a better and better person.
I like to add to it the Buddhist philosophy. Happiness is enjoying what you have, and not yearning after what you don't have. Sadness, is the reverse. Maybe there is a balance between the two ?