For years I watched my dad smoke, and when I went to school - most of my friends start. For those years I hated the idea with a passion, and questioned why anyone would want to do such a thing...
... until I found myself constantly, deeply upset and fighting extremely anxious turns due to my work and home life - at which point I thought "anything that kills me quicker" and gave it a go one day. Since then I have found no better way to temporarily switch off my anxious tick for half hour, even though its gross and smelly. Granted I usually smoke one a day, with gaps of days in between sometimes - but there are days when I will knock out a 20 deck when its bad. I keep it in check by only ordering high quality cigs online, Sobranie usually - that way if i go to hard, I have to go cold turkey for 3 days until i can get hold of more - by which time the cravings pass.
And yeah, I know its bloomin' stupid, i'm 24 and my sister is a doctor - so I know what I am lining up for....