How does addiction work?[addicts help!]?

I once tried getting addicted to cigarettes just to show that I was tough enough to quit. I knew someone who smoked half his life. Then he decided to stop one day and he stopped. I got bored of smoking the cigs and having stinky clothes so I stopped.

Ppl get addicted to various things. Drugs, booze, cigs, food, and even cutting their skin. Why can't you just stop? It isn't like these things can happen on accident, they are concious acts. For instance, someone on here asked how to stop cutting. And I am thinking it is as easy as not pushing a razor into your skin. It isn't like you can accidentally slice your skin over and over with a razor.