Although starting to smoke is a total moron thing to do, there may be less irrationality present in pursuing an existing addiction than commonly believed. Someone who craves nicotine has the choice of attempting to ignore the craving, which has all kinds of bad, immediate consequences (irritability, distraction, twitchiness, insomnia, flu symptoms, sore mouth, sore throat, cough, headache, intestinal protestations, etc.) until you keep it up for a good long time, or giving into it, which has (per cigarette) very small and distant negative consequences (tiny increase in risk of assorted diseases which might kill you or not).

It's possible I'm only defending this because I have the exact same problem with chocolate. (I can resist my chocolate cravings, but only if I'm not doing anything else, and so far I don't have a few weeks where I can be afford to be totally out of commission to detox from delicious chocolatey goodness in the hopes that this would make the cravings go away forever.)