Ewalt begins by explaining the concepts behind a D&D game. Unlike a board game, where the action is very predictable – you move forward one square and may land on another square that always tells you to "Lose a turn" – a D&D game can be different every time. Each player portrays a different character, usually a traditional fantasy archetype like an elf or dwarf, while a player who is known as the Dungeon Master gives the players instructions. The DM has thought up the storyline for the game already – for example, the players go into a cave looking for treasure. A storyline can go on for a very long time. D&D-ers sometimes decide to have their game be a "campaign," meaning that the story they're acting out through the game will continue the next time they meet up. Campaigns can go on for months or years, says Ewalt. "Players are both audience and author in D&D," he writes. "They consume the DM's fiction but rewrite the story with their actions."