Robin reminded me of a great John Wayne quote the other day, and I went to find the source of it. Turns out it came from one of his movies:
"Life is tough, but it's tougher if you're stupid." - Sgt. Striker, "The Sands of Iwo Jima" (1949)
That's a good admonition for everyday life, but that's also a great element for stories, because writers like me often depend on our characters ignoring this trope.