So open-minded that our brains fall out

I've been thinking about this a lot lately, and finally tracked down the original source:

Let us keep our minds open, by all means, as long as that means keeping our sense of perspective and seeking an understanding of the forces which mould the world. But don’t keep your minds so open that your brains fall out! There are still things in this world which are true and things which are false; acts which are right and acts which are wrong, even if there are statesmen who hide their designs under the cloak of high-sounding phrases.

— Walter Kotschnig, November 8, 1939

Coincidentally, I'm part way through Factfulness, by Hans Rosling.