Peter D. Ouspensky (March 4, 1878–October 2, 1947), (Pyotr Demianovich Ouspenskii, also Uspenskii or Uspensky, Пётр Демья́нович Успе́нский), a Russian esoteric philosopher known for his expositions of the early work of the Greek-Armenian teacher of esoteric doctrine George Gurdjieff, whom he met in Moscow in 1915. Ouspensky studied the Gurdjieff System directly under Gurdjieff's own supervision for a period of ten years, from 1915 to 1924. Ouspenky's book "In Search of the Miraculous" is a recounting of what Ouspensky learned from Gurdjieff during those years.
"In these studies of Kabbalah, we need to be practical; there are authors who write marvels, but when one looks at them, one realizes that they have not lived what they have written; they did not experience it in themselves, and that is why they are mistaken. I understand that one must write what one has directly experienced by oneself. I have proceeded in this way for my part."