In the practice of meditation, you are trying to breathe out and in and simply exist. In doing so, you might discover a hollowness in yourself, a vacuum, a kind of foolishness, as you realize that you may not actually exist. However, “hollow” implies a solid shell, but here one’s basic substance is not there at all. You don’t wear solid clothes, but clothes made out of feathers—and everything falls apart when you begin to ruffle.
From The Path of Individual Liberation: Volume One of The Profound Treasury of the Ocean of Dharma by Chögyam Trungpa, page 522