simply put, your mind gets addicted rather than your body, there can be withdrawl symptoms and all that shit, physically addictive and psychologically addictive shit can share the exact same properties and everything, the only thing that seperates them is that physically has some type of chemical or something in that your body gets used to and gets thrown off when it's taken away, where as psycholgically there is no chemical to get addicted to, therefore any thrown off symptoms you get when quit is all in your head.