What's the one investing quote you always come back to?

Markets can be exciting, stressful, and unpredictable. During those moments, a simple quote can sometimes help keep things in perspective.

Whether it's from Warren Buffett, Charlie Munger, Peter Lynch, or someone less famous, what's one investing quote that has genuinely influenced how you invest?

More importantly, how has that quote changed your decision-making during market highs and lows?