Willpower is the muscle of the mind
In the 8 Limbs of Yoga, the sixth limb is Dharana, which means concentration. Concentration is a vital ability in your yogic practice. In fact, it’s a vital ability in anything you do in life. One of my many teachers- Dandapani, defines concentration like this “Concentration is the ability to keep your awareness at one point for an extended period of time”. He also says that if you water your garden, both flowers and weeds will grow, because water does not differentiate the two. The same way energy does not differentiate between positive and negative. Our awareness is energy, and whatever you want in life, it requires some energy. Your ability to concentrate your energy on something determines how fast and well it will grow.
If the mind had a muscle it would be called willpower. Whenever you try to meditate and your mind drifts off, it is your consciousness that notice and your willpower that draws is back to your point of focus and keeps it there. Concentration is therefor a product of willpower.
Let’s say you watch a movie. The producer of the movie wants to take you on a journey. He takes your awareness to different places that makes you happy, sad, angry, annoyed, compassionate and so on. With great willpower, you don’t need a movie to take you on such journeys. You can use your willpower to get to those same places by yourself.
Just as it takes willpower to do something we don’t want to do, it is the same muscle that brings your awareness away from stressful places to peaceful places. When we’re anxious our minds are drawn to everything that may go wrong, but with willpower we can take back control and calm our minds simply by changing our place of awareness.