When I was a young monk, I wondered why the Buddha kept practicing mindfulness and meditation even after he had already become a Buddha. Now I find the answer is plain enough to see. Happiness is impermanent, like everything else. In order for happiness to be extended and renewed, you have to learn how to feed your happiness. Nothing can survive without food, including happiness; your happiness can die if you don’t know how to nourish it. If you cut a flower but you don’t put it in some water, the flower will wilt in a few hours. Even if happiness is already manifesting, we have to continue to nourish it. This is sometimes called conditioning, and it’s very important. We can condition our bodies and minds to happiness with the five practices of letting go, inviting positive seeds, mindfulness, concentration, and insight.
– Thich Nhat Hanh, in “No Mud, No Lotus: The Art of Transforming Suffering”