The key to happiness is gratitude. Gratitude means that we allow reality to be just as it is. When we are grateful, we do not have expectations as to how things should be. We are happy and grateful for the way things are. Since our experience in the world is a reflection of our inner state, when we are grateful, the Universe responds by providing abundance.
When we are in a constant state of desiring things, the Universe responds by not providing what we want. This creates a constant cycle of dissatisfaction. When we are grateful for whatever we have, even if what we have is comparatively meager, the Universe responds by providing what we need for our development and happiness. Donald Trump is a very poor man indeed, because he never experiences satisfaction. He is always longing for more in order to fill the hole inside himself, which can never be filled by things.
Let's be grateful for what is.