I vaped unflavored nicotine for about 2 years. Intermittent at first, heavy daily use during the second year, equivalent to a pack of cigarettes per day or more. I quit because enjoyment decreased to the point where it was no longer worth the hassle.

I experienced zero addiction for the first three months, and even after the full two years addiction was mild. I reduced my dose gradually over two weeks. There were no physical withdrawal symptoms, and only minor craving which went away after a few months abstinence. I'm no expert on heroin addiction, but I find it hard to believe it's equal to nicotine. Perhaps whole tobacco would be different.

No, the difference is, at least from what I've seen (am not sure if the research supports this, but it would be interesting if it did not), some people (like myself) seem to be more susceptible to smoking addiction than others. I know quite a few people who have no trouble smoking intermittently, with months in between, and then quitting with hardly any effort. Maybe they just have more resolve or willpower, but I've seen them smoke more than enough to "catch" the addiction like I did, then stop, never really getting stuck into a daily habit. Yes I'm jealous :) On the other hand, I don't want to smoke just "occasionally" either, I just want to quit.