You start doing the addictive behavior to feel good and then your receptors get overloaded with dopamine, then you stop doing the addictive thing and some of the receptors have shut down and you don't have enough dopamine to feel good. So then you feel bad and go back to the addictive behavior to get more dopamine. The strange thing is that it works with what we think of as uppers and downers and whatever you call gambling - sidewaysers.