Some things like heroin and alcohol cause chemical addiction. The body adapts to the chemical and comes to require it. This can be a very tough addiction to break due to withdrawl symptoms. There are people who've been taking Methodone treatments for decades because skipping them will cause them to experience heroin withdrawl.

There's also psychological addiction where people come to rely on something more as a matter of habit than of chemical addiction. I've discussed this with quite a few smokers who tend to smoke whenever they have a cup of coffee or during similiar habits.

It's quite likely that many, perhaps most, smokers do become chemically addicted to nicotine. All I'm suggesting based on the personal stories of a few individuals is that perhaps some people don't become chemically addicted to nicotine. Those people managed to quit a decades-long smoking habit suddenly without any form of withdrawl.