My 6th Grade teacher would put a weekly quote up on the chalkboard (before whiteboards) each week. This one stuck with me.
"Better to remain silent and be thought a fool than to speak out and remove all doubt."
Here are a few more from Mr. Lincoln:
"I have been driven many times to my knees by the overwhelming conviction that I had nowhere to go. My own wisdom, and that of all about me, seemed insufficient for the day. "
"I care not much for a man's religion whose dog and cat are not the better for it."