Never give in - never, never, never, never, in nothing great or small, large or petty, never give in except to convictions of honour and good sense. Never yield to force; never yield to the apparently overwhelming might of the enemy.
Winston Churchill, 29 October 1941
never yield to the apparently overwhelming might of the enemy.
I'd like to add to that:
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).