On a recent Late Late Show, host James Corden brings up D&D with his guest, Thomas Middleditch (Silicon Valley). Middleditch and his D&D group have just wrapped up a three year campaign and Corden asks how could a game of D&D go on for so long and why? Middleditch responds:
Do you have the courage to imagine, James? Then, you can get 4-6 other grown adults to sit around a table and all try to imagine the same thing together. And, when there's a contest for anything you want to happen, you roll them bones, then you can play Dungeons & Dragons for three years. We told a fantasy epic that is akin to Lord of the Rings that is entirely our own and exists only in our minds. It was a very, very important story that was told only for the six people who were in our group.
Middleditch goes on to do the work of the Gods of the Multiverse by saying that you really can't explain your D&D campaigns to others who weren't there and you shouldn't try. (Yes, for the love of Greyhawk, keep the ribald exploits of your Tiefling rogue to yourself).