For seriousness seeks to exclude play, whereas play can very well include seriousness.
Quotes by Johan Huizinga
All play has its rules. They determine what “holds” in the temporary world circumscribed by play. The rules of a game are absolutely binding and allow no doubt. Paul Valéry once in passing gave expression to a very cogent thought when he said : ” No scepticism is possible where the rules of a game are concerned, for the principle underlying them is an unshakable truth.”