Everyone is different and there are a variety of factors. Perhaps I don't have an addictive personality trait...I can smoke for weeks, drink for days and then quit without having an urge to fulfill a need. I've smoked as long as 4 years straight, never skipping a beat and outside of some sleeplessness for a couple of days, I was straight. Others can try tobacco, herb, alcohol, or other drugs and convince themselves that they need it. It's mind of matter.