“Wisdom comes to those who learn nothing, unlearn everything.
That transformation is the consequence not of something done, but of something dropped.”

The Ringworld Throne (1996)

Source: Falling Upward

A favourite comment, inscribed on his memorial at Ealing, quoted in Nature Vol. XLVI (30 October 1902), p. 658
1890s

Emperor Has No Clothes Award acceptance speech (2003)
Context: I am a reasonably emotional person, and I see no reason why that's incompatible with being a scientist. Even if we learn about how everything works, that doesn't mean anything at all. You can reduce how an impala leaps to a bunch of biomechanical equations. You can turn Bach into contrapuntal equations, and that doesn't reduce in the slightest our capacity to be moved by a gazelle leaping or Bach thundering. There is no reason to be less moved by nature around us simply because it's revealed to have more layers of complexity than we first observed.
The more important reason why people shouldn't be afraid is, we're never going to inadvertently go and explain everything. We may learn everything about something, and we may learn something about everything, but we're never going to learn everything about everything. When you study science, and especially these realms of the biology of what makes us human, what's clear is that every time you find out something, that brings up ten new questions, and half of those are better questions than you started with.

Source: Brida

From 'Address at Holy Cross' (25 June 1919), published in Have Faith In Massachusetts: A Collection of Speeches and Messages (2nd Ed.) http://www.archive.org/details/havefaithinmassa00cooluoft, Coolidge, Houghton Mifflin, p. 231.
1910s, Address at Holy Cross (1919)