"How vain it is to sit down and write when you have not stood up to live."
dreaming while knowing that you are dreaming. The term was coined by Frederik van Eeden who used the word "lucid" in the sense of mental clarity. Lucidity usually begins in the midst of a dream when the dreamer realizes that the experience is not occurring in physical reality, but is a dream. Often this realization is triggered by the dreamer noticing some impossible or unlikely occurrence in the dream, such as flying or meeting the deceased. Sometimes people become lucid without noticing any particular clue in the dream; they just suddenly realize they are in a dream.