Using willpower to quit involves giving up smoking even though deep down you don't really want to. Think about that. We have an inbuilt resistance to being told to do things that we don't want to do, or don't think we should do - it's a basic survival instinct. The majority of people who try to stop smoking, particularly on their first attempt, are pulled into the myth that it will be unpleasant and difficult, and it will be if you use willpower. You are fighting your own instincts and creating an internal battle with yourself as the (formidable) opponent. So forget willpower and start thinking about what you really want.
Choice means giving up smoking because you want to give up. And when you reach the point when you stop because you want to, you'll find that there's no resistance left - nothing to fight against. This is the critical point when it becomes easy. Stop making yourself do it and start wanting to do it.
For further ideas and advice and ways to stop smoking, visit the substantial resources section of this site - Stop Smoking Resources