The engineer, weary of design tradeoffs and wary of uninformed decisions, asked for more details. "Sure," replied the Gatekeeper. Here is the elevator. You can ride up and see Heaven and down to see Hell. Take your time and make your choice. But choose wisely, there is no turning back!"
So the engineer rode the elevator up and took a look at Heaven. He saw the angels playing on their harps and the beatific look on the faces of the faithful, blissfully flitting back and forth among the clouds. "Well, that looks about like what I expected," he said to himself. "Let's go take a look at the alternative." So he rode down the elevator to the floor labelled "HELL" and looked around there. To his delight he found sandy beaches, beautiful women, snow-capped mountains in the background, and parties going on all over. Returning to the Gates, he had no problem informing the Gatekeeper of his decision.
"Heaven looks fine, but pretty boring to me. Hell is what I have always dreamed of! Let me in." The Gatekeeper handed him an entry pass and the engineer went back down the elevator to take his place in Hell. But to his surprise, the sun had gone out, the snow had melted and the parties were over. There was fire and brimstone, snakepits swarming with vipers, fiends torturing sinners, and devils tormenting babies. "Wait!" he cried as two monsters hauled him off to the chambers of eternal agony. "What happened to the beach parties, fun and sunshine I saw before?"
"Oh," replied the Devil. "That was just the demo."
Attribution unknown[I've seen at least one variant of this, replacing the engineer with Bill Gates]