I smoked cigarettes for about a year, and I realized that it would quickly become a problem if I didn't stop immediately. The nicotine withdrawals were really easy to ignore, actually (benefit of only smoking for a year I guess). The problem was the random triggers. I used smoking as a time filler, and as someone who is lonely and bored 99% of the time I could smoke a lot. After work, before bed, after dinner, in the mornings, with coffee, with beer - for a while even the thought of those things made me want a cigarette. I had to cut out coffee and beer for about a month before I could safely have them again.

This experience made me realize that I use things as crutches, as things to fill time when I'm lonely and don't know what to do. Things that aren't technically addictive like marijuana would be problematic for me because I know that if I like it, I would do it almost constantly. The only thing preventing alcohol from being a problem is the fact that I hate getting drunk. I never understood why people like that feeling.

So basically, it's just the self awareness that I WILL turn anything into a serious addiction given the chance. I don't want that to happen, so I won't give myself the chance.

tl;dr fear.