André Gide, The Counterfeiters (1925)

It seems to me sometimes that I do not really exist, but that I merely imagine I exist. The thing that I have the greatest difficulty in believing in, is my own reality. I am constantly getting outside myself, and as I watch myself act I cannot understand how a person who acts is the same as the person who is watching him act, and who wonders in astonishment and doubt how he can be an actor and a watcher at the same moment.