We all experience two kinds of thirst in life, and unless we understand the difference between them, we will always be frustrated.
The first kind of thirst is horizontal thirst. We thirst for, we desire, the good things of this earth: food, drink, companionship, fun, entertainment, a nice house, a good income, success at work or school.
It's part of our nature to desire these things; there's nothing wrong with them. But we also have another kind of thirst - vertical thirst.
This is a deeper thirst, a deeper desire. It's a desire for meaning and purpose. This desire is also built into our nature. There is nothing we can do to destroy it, just as there is nothing we can do to destroy our natural desires for food and water.
But unlike horizontal thirst, our vertical thirst cannot be satisfied by our own efforts. Only God himself can satisfy it. And he created us like that on purpose.
It's as if he put a homing device in the very core of our being, and it constantly draws us towards him, towards intimate, personal contact with his eternal, transcendent love.
This is why even when all of our horizontal thirsts are satisfied, when we have money, success, and pleasure, we are still restless.
Our deeper, vertical thirst can't be satisfied by things of this world. As the Catechism puts it: "Man is made to live in communion with God, in whom he finds happiness" (#45).
The meaning and purpose which alone will give us true happiness comes from friendship with God in Christ, not from worldly success, pleasures, and human relationships.
When we forget that, when try to satisfy our vertical thirst with horizontal stuff, we put ourselves on the road to frustration, tragedy and disappointment.