Most gods throw dice, but Fate plays chess, and you don't find out 'til too late that he's been playing with two queens all along. ~Terry Pratchett
Also known as being a DM. (Dungeon Master) -- Anon Guest
Imagine a game so complicated that even the experts have to look up the rules. It is not just played with dice, but also cards, charts, tables, books, miniatures, and a hell of a lot of imagination. There is only one person at the game table who knows anything about what's going on, and that is the holder of the core of the story. They know most of what's going to happen. Well. What's most likely to happen.
The one thing they don't have control of is what the players are going to do. Because everyone who plays this game is a chaos demon in roughly humanoid form. They have a set of rules, too. A set of rules almost as complicated as the entire game, with permutations and corollaries so complicated that nobody could keep track of them all. Player choices leading to potentially infinite customisation not limited to the character's appearance, but also throughout the game.
The game can last for years. Groups meeting to play on a semi-regular basis. Play interrupted by life events, by colds and other virii, by children and the associated shenanigans, by spouses, by family, by work... but they keep returning to play. A game that can involve pop culture, dirty jokes, incidental weaponised singing - both in-game and out - research, improvisation, and massive amounts of bullshit made up on the fly. No one session is completely predictable. No game is ever played the same way by any group of players. It's no surprise that something this phenomenally complicated is also something invented and enjoyed by Humans.