Look sharply after your thoughts. They come unlooked for, like a new bird seen on your trees, and, if you turn to your usual task, disappear; and you shall never find that perception again; never, I say — but perhaps years, ages, and I know not what events and worlds may lie between you and its return!
Journals of Ralph Waldo Emerson 1864-1876, October 1872 (p. 365), Houghton Mifflin Company. 1911