Authors:

If the game designer produces more content than he can consume per month, some fraction of the people will say more quests, more tests, more challenges, more whatever, and they will be compelled by it.

"Davos Interviews: Max Levchin Says Slide Now Makes Almost All Of Its Money From Virtual Goods". Interview with Erick Schonfeld, techcrunch.com. February 1, 2010.
If the game designer produces more content than he can consume per month, some fraction of the people will say more quests, more tests, more challenges, more whatever, and they will be compelled by it.