“215. Into a mouth shut flies flie not.”

Original quote:
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)
Misattributed

Source: A Day No Pigs Would Die

Source: The Wise Man's Fear

Source: …And All the Stars a Stage (1971; [serialized in 1960]), Chapter 13 (p. 180)

Okay. When we have the chance, if this stuff all falls into place, that The Blaze is going through right now, I'm telling you — miracles, absolute miracles.
2014-02-12
The Glenn Beck Program
Radio, quoted in * 2014-02-12
Beck: God Told Me To Sit Down And Shut Up Because He Has 'Absolute Miracles' In Store For The Blaze
Kyle
Mantyla
RightWingWatch
http://www.rightwingwatch.org/content/beck-god-told-me-sit-down-and-shut-because-he-has-absolute-miracles-store-blaze
2014-02-05
2010s, 2014

Cited as an example of "What Mark Twain Didn't Say" in Mark Twain by Geoffrey C. Ward, et al.
Misattributed
Variant: It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.