"Everyone wants to understand art. Why don't we try to understand the song of a bird? Why do we love the night, the flowers, everything around us, without trying to understand them? But in the case of a painting, people think they have to understand. If only they would realize above all that an artist works of necessity, that he himself is only an insignificant part of the world, and that no more importance should be attached to him than to plenty of other things which please us in the world though we can't explain them; people who try to explain pictures are usually barking up the wrong tree."
-- Picasso

True. But I think people have wondered why they love the night, the flowers, and everything around them.
Doesn't someone wonder why we feel happy when we make other people happy? If it's because there is some God and a force that creates good and evil, where good brings some kind of inner joy in us, and where good can be done by spreading joy, then that might be one explanation. And if there is no God, or if there isn't such a simple divide between good and evil, if those concepts don't really exist in an absolute form, then why should good be more innate that we should be happy to smile at someone else? Or maybe we're not only happy that way. Some feel happy when they watch someone's downfall too. Why should doing good feel good? Just as why should we love the night?