Why can't a person quit a habit if they don't really want to?
A person cannot quit a habit without genuine desire because the will to quit must come before the act. If someone admits they do not really want to quit, then quitting will not happen; the wanting has to precede the doing.
Les explains that when people talk about smoking and say they wish they could get rid of the habit, he asks whether they really want to quit. If they answer no, not really, he says they are guaranteed not to quit, because the desire must come before the action. The same principle appears in believing: people say they cannot believe, but the real issue is that they do not want to.