An open mind is really a mark of foolishness, like an open mouth. Mouths and minds were made to shut; they were made to open only in order to shut.

For my friend said that he opened his intellect as the sun opens the fans of a palm tree, opening for opening's sake, opening infinitely for ever. But I said that I opened my intellect as I opened my mouth, in order to shut it again on something solid. I was doing it at the moment. And as I truly pointed out, it would look uncommonly silly if I went on opening my mouth infinitely, for ever and ever. | The Extraordinary Cabman, one of many essays collected in Tremendous Trifles (1909)