“Ardently alert means that when the mind is staying with the breath, you try to be as sensitive as possible in adjusting it to make it feel good, and in monitoring the results of your efforts. Try long breathing to see how it feels. Try short breathing, heavy breathing, light breathing, deep, shallow. The more refined you can make your awareness, the better the meditation goes because you can make the breath more and more refined, a more and more comfortable place for the mind to stay. Then you can let that sense of comfort spread throughout the body. Think of the breath not simply as the air coming in and out the lungs, but as the flow of energy throughout the whole body. The more refined your awareness, the more sensitive you can be to that flow. The more sensitive you are, the more refined the breath becomes, the more gratifying, the more absorbing it becomes as a place to stay.”

"Meditation: The How and the Why" (2003)