The importance of NPCs (Non-Player Characters, or "extras". -T.)
In D&D NPCs are the people who do all the mundane things of the world. From washing your horse, to planting corn, to being your lover. Most people in the D&D world are NPCs and will never go on a great adventure. If you treat an NPC badly they may steal your horse, poison your mead, or even GASP, stop being your lover. No one can get far without the support of the NPCs
Most people in the real world are NPCs also. Mundane people who lead mundane lives. But if you treat them wrong they might, key your car, spit in your beer, or GASP, stop being your lover. (Once again some things are truly universal).
-from All I ever needed to know, I learned playing Dungeons & Dragons.
I'm geeky enough to admit that that's pretty funny, right there.