5 Creepy Ways Video Games Are Trying to Get You Addicted

http://www.cracked.com/article_18461_5-creepy-ways-video-games-are-trying-to-get-you-addicted.html

He invented the "Skinner Box," a cage containing a small animal that, for instance, presses a lever to get food pellets.

If you want to make him press the lever as fast as possible, how would you do it? Not by giving him a pellet with every press--he'll soon relax, knowing the pellets are there when he needs them. No, the best way is to set up the machine so that it drops the pellets at random intervals of lever pressing. He'll soon start pumping that thing as fast as he can. Experiments prove it.

They call these "Variable Ratio Rewards" in Skinner land and this is the reason many enemies "drop" valuable items totally at random in WoW. This is addictive in exactly the same way a slot machine is addictive. You can't quit now because the very next one could be a winner. Or the next. Or the next.