This is something I can identify with, as it's true of all the RPGs I really enjoy. Being constrained by either expectation (e.g., it's D&D so there will be a dungeon) or starting point (e.g., it's D&D so you can be a fighter, a wizard, a cleric, a dwarf, or an elf) forces both players and DMs to continually re-invent, rejig, and genuflect their games and characters in ways in which a blank slate somehow could not. (At least in theory. There are of course plenty of players who end up being Bob the Fighter in every game.) If you're playing D&D and you know therefore there are to be dungeons, you put in the extra effort to make those dungeons unique and interesting so they don't come across as old. If you're playing D&D so you know you're going to end up being the cleric, you invent some weird and wonderful new deity, religion and trappings to keep things fresh.
RPGs accomplish creativity through constraint in three different ways:
- The Warhammer Fantasy Roleplay Model. This uses hardcore randomness in character generation to force players into boxes they weren't expecting to be put inside. They then have to shape their character on unsure and unexpected footing.
- The BECMI D&D Model. This allows some choice of role, but the roles are highly rigid archetypes that allow for little variation. This forces players to come up with cosmetic and character-based variety; if you have to be an elf you're going to play an elf who is scared of water, whose culture is modelled on Turkish horse nomads.
- The Pendragon Model. This is the ultimate in constraint: in its purest form Pendragon insists that the players will all without exception take on the role of squires about to be knighted and taken into the service of King Uther (or King Arthur). Players therefore come up with highly creative means of distinguishing themselves from each other in looks, personality, abilities and history.