Updated: Sep 6, 2019
The greatest expression of happiness is the desire to play. Playfulness means being willing to surprise and be surprised; it means having some sense of self, but not a strict one. It means throwing something out to others and waiting, in openness, to see what will come back. And then acting from there. There is no strict plan, though plans may be created, dissolved, or changed.
There is perhaps a preconception that adults are the ones who destroy the world of play of the children, by requiring that the children stop playing and be responsible and docile; that they focus on more consequential things. This may be true in some cases, but it is also true that the desire to play becomes attenuated because playing itself can hurt; children hurt other children. Besides physical pain, there is also just the hurt of being defined in an unpleasing or inferior way by others because they are more powerful in the game or in "play" than oneself. As certain children manage to get more quickly integrated into the adult world (whether into its organized or more seamy sides), their power relative to their peers, and therefore also ability to hurt the latter, increases, thus obliging their weaker peers to search for other sources of strength in the world too. So perhaps the question is not, how can we better appreciate the children's world of play? but rather, how can we better understand the very real effect, and function, that play has?
Ultimately the adult world is really what the world of play has evolved into – it is what grown-up children have done to keep playing while also taking into account the dangers of uncontrolled play. There is a code of conduct that everyone has to continuously remind everyone else of (such as to help the elderly, be polite, respect property) and which is to some degree enforced by a government, to prevent reckless spontaneity from taking over. On the other hand, there is the uncomfortable fact that the game has become even more real than it ever was. Losers are real losers now; winners are real winners. One sometimes wants to cry out, “But this is just a game! It could have turned out otherwise,” yet one knows that the implied answer is "It may be a game, but there's no reality outside of it, anyway."