Can I break a bad habit overnight?

According to Lynn Harris, Yes.
How? Hypnotherapy.

She shared her story of quit nail-bitting after a two-hour hypnotherapy session.
I've been attending hypnosis groups to experience it myself. After a few sessions, I'm still on the fence. But since hypnosis works directly with the subconscious mind, it is very likely the shortest path to changing your habit.

Whether you go to a hypnotherapist or DIY at home following a tape. The soothing voice is only there to guide you. It's you yourself who is doing all the work. Remember "The Secret"? The key concept is Self-affirmation. Positive thinking in your sub-conscious mind is critical in shaping your your behavior.

In previous posts, we talked about using imagination to help forming the new habit. It's actually the same theory.

The first time it worked for me was in high school. I had this vault-phobia in gym classes. No matter how many times I practiced, the idea of jumping over it always make my legs quiver. The night before the exam. I lied in my bed and pictured myself jumping over it with the precision of the gold medal winner. The next day, my body simply surprised myself with a beautiful finish effortlessly. Now I do the self-talk before important presentations and it works every single time.

Will it work for you? You'll never know until you try it.