The premise is this: Why struggle to do something when you can simply make it automatic?
The basic steps of habit formation are to choose a trigger, associate it with a behavior, and reward yourself for doing the behavior. For example, if you want to exercise more often, you could put your sneakers in the kitchen cabinet next to your cereal. This will remind you to go for a run before breakfast, even as your tired self is starting to reach for the Cheerios. After your run, reward yourself with your favorite coffee on the way home. Repeat often enough, and voila, a habit is born. Exercise will soon become automatic.
If you're laughing, I don't blame you. If only it were that easy to change what we do.
Unfortunately, we aren't so easily programmed (or deprogrammed). Even if it were simple to build new habits, it doesn't guarantee that they will replace destructive habits. The process of overcoming a bad habit typically requires a lot more than building a positive new habit. You need skills for tolerating distress, cravings, anxiety, and discomfort. You need self-compassion for setbacks. You need social support or role models. You need a certain amount of mindfulness and motivation to recognize when you might be acting in ways counter to your goals -- and recognize new, unplanned opportunities to make progress on your goals. And yes, you will need some willpower for when you are most overwhelmed by desire, stress, anxiety, boredom, or self-doubt.
I recently gave a talk on this problem to a Habit Formation group. It's called "Are You Sure You Want a Habit?", and you can watch it below. In it, I describe the main ways habit formation fails, especially when it comes to what I call "really freakin' hard changes" like addiction, weight loss, or overcoming anxiety-based procrastination.