C. S. Lewis and running towards a cliff

When the whole world is running towards a cliff, he who is running in the opposite direction appears to have lost his mind.

Attr. C. S. Lewis

Attributed to CSL, but not by him. The invaluable William O’Flaherty of “Confirming C. S. Lewis” says on his FB group that it can’t be found in Lewis and that its earliest appearance as a CSL “quotation” is 1997. O’Flaherty has digital editions of Lewis’s oeuvre, so he is quite likely correct. For what it’s worth, I looked around a little on Google Books and couldn’t find it in Lewis either.