Ars longa, vita brevis (Hippocrates, ancient Greek physician) Life is short, the art [of medicine] is long.
Quod scripsi, scripsi What I have written, I have written. (The Bible, John 19:22)
Animal implume, bipes (Plato) A two-legged, featherless animal.
Cogito, ergo sum (Rene Descartes - French philosopher and writer) I think, hence I am.
Ne puero gladium (Do not give) a sword to a boy.