I came across an excerpt of Thích Nhất Hạnh from his book No Mud, No Lotus, in which he says that happiness must be nurtured in order to sustain (full text is here, the excerpt can also be found here):
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.
Earlier in the book (here), he relates this idea to the Buddha:
The Buddha said that nothing can survive without food. This is true, not just for the physical existence of living beings, but also for states of mind.
This surprised me a bit, as I was under the impression that happiness emerges when one frees himself (even momentarily, e.g. during meditation) from suffering - and not that it should be pursued as a goal.
I read (in Wikipedia) that Thích Nhất Hạnh's teaching combines various sources, and I'd like to know if this idea - that happiness must be nurtured - can be traced to a certain Sutra, or just scattered texts, in the canon?