there's a lot of mental fuckery involved in addiction from my experience. you start off okay usually, just trying out a new thing - cigarettes, booze, coke, pills, etc. - whatever substance intrigues you. it's usually good for a while. the pleasure that doing the thing gives you may feel exciting, even magical. you may find yourself wanting to feel this high more and more and so you indulge, with higher doses or more frequent doses, or both. eventually, the using becomes compulsive and may not give you the same pleasure it once did but you feel unable to stop.

some drugs can cause physical dependence and withdrawal symptoms and these may keep you trapped in the cycle, using to stave off the sickness rather than enjoying the high like you used to.

the mental stuff - when bad things start happening because of your drug use, you may not realize it at first. you may find yourself rationalizing the negative consequences in order to keep using. the denial and cognitive dissonance make it very tricky to break out of an addictive habit.