“When in doubt, look intelligent.”

"The Protestant Mystics", p. 51
Forewords and Afterwords (1973)

Variant: Do I look feeble to you"
"Actually, yes."
"Well, looks can be deceiving. For instance, when I met you, I thought you look reasonably intelligent.
Source: Unwind

The Freethinker (1970), G.W. Foote & Company, Volume 90, p. 147.
Date unknown

Variant: The problem with the world is that the intelligent people are full of doubts, while the stupid ones are full of confidence.

Often paraphrased as "The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts."
Compare: "One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision." B. Russell, New Hopes for a Changing World (1951). Compare also: "The best lack all conviction, while the worst / Are full of passionate intensity." W. B. Yeats, The Second Coming (1919).
See also: Dunning-Kruger effect, Historical Antecedents https://en.wikipedia.org/wiki/Dunning–Kruger_effect#Historical_antecedents.
1930s, Mortals and Others (1931-35)

Rules for success

Google It: Total Information Awareness, 2016

Cette harmonie que l’intelligence humaine croit découvrir dans la nature, existe-t-elle en dehors de cette intelligence ? Non, sans doute, une réalité complètement indépendante de l’esprit qui la conçoit, la voit ou la sent, c’est une impossibilité.
Introduction, p. 14
The Value of Science (1905)

Mont Saint Michel and Chartres (1904)