"Doubt is not a pleasant condition but certainty is an absurd one."
- Voltaire, 1694-1778

"I have approximate answers and possible beliefs and different degrees of certainty about different things, but I'm not absolutely sure of anything..."
- Richard Feynman, 1918–1988;

"If you gaze long into an abyss, the abyss will gaze back into you."
- Friedrich Nietzsche

"Errors like straws upon the surface flow:
Who would search for pearls must dive below"
- John Dryden

"Your vision will become clear only when you look into your heart. Who looks outside, dreams. Who looks inside, awakens."
-Carl Jung