"When I was a boy of 14, my father was so ignorant I could hardly stand to have the old man around. But when I got to be 21, I was astonished at how much the old man had learned in seven years." - Mark Twain
“If the doors of perception were cleansed every thing would appear to man as it is,Infinite. For man has closed himself up, till he sees all things thro' narrow chinks of his cavern.” - William Blake This is the line that gave Aldous Huxley the title of a book about his experience with mescaline called The Doors of Perception which in turn inspired a young poet to name his band simply The Doors.
And my wife's least favorite, which is actually a mash up of two that I love to use to warn young men entering the world of pubescent females....
"Never argue with a woman, it's like trying to teach a pig to sing. It wastes your time and annoys the pig."