Game design ideas gain value, sophistication, and meaning only when they are playtested. The hard work of the process, the actual game design itself, happens during the iterative process, not the concepting process that proceeds it.
Quotes by Eric Zimmerman
Rules might not seem like much fun. But once players set the system of a game into motion, play emerges. And play is the opposite of rules. Rules are fixed, rigid, closed, and unambiguous. Play on the other hand is uncertain, creative, improvisational, and open-ended. The strange coupling of rules and play is one of the fascinating paradoxes of games.