“General principles are not the less true or important because, from their nature they elude immediate observation; they are like the air, which is not the less necessary because we neither see nor feel it, or like that secret influence which binds the world together and holds the planets in their orbits.”

Duty Surviving Self-Love (1826)
Context: O wiselier then, from feeble yearnings freed,
While, and on whom, thou may'st — shine on! nor heed
Whether the object by reflected light
Return thy radiance or absorb it quite:
And tho' thou notest from thy safe recess
Old Friends burn dim, like lamps in noisome air,
Love them for what they are; nor love them less,
Because to thee they are not what they were.

"Our Inner Ape: A Leading Primatologist Explains Why We Are Who We Are" (2005), p. 243
Context: In 1879, American economist Francis Walker tried to explain why members of his profession were in such "bad odor amongst real people". He blamed it on their inability to understand why human behavior fails to comply with economic theory. We do not always act the way economists think we should, mainly because we're both less selfish and less rational than economists think we are. Economists are being indoctrinated into a cardboard version of human nature, which they hold true to such a degree that their own behavior has begun to resemble it. Psychological tests have shown that economics majors are more egoistic than the average college student. Exposure in class after class to the capitalist self-interest model apparently kills off whatever prosocial tendencies these students have to begin with. They give up trusting others, and conversely others give up trusting them. Hence the bad odor.

Discourse Delivered at the Royal Society (30 November 1825), published in Six Discourses delivered before the Royal Society, at their Anniversary Meetings, on the Award of the Royal and Copley Medals, preceded by an Address to the Society on the Progress and Prospects of Science (1827); also in The Edinburgh Review Or Critical Journal (October 1827)
Context: Fortunately science, like that nature to which it belongs, is neither limited by time nor by space. It belongs to the world, and is of no country and of no age. The more we know, the more we feel our ignorance; the more we feel how much remains unknown; and in philosophy, the sentiment of the Macedonian hero can never apply, — there are always new worlds to conquer.

Section 94
The True Believer (1951), Part Three: United Action and Self-Sacrifice

Plato, Phaedo

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.

"On Knowledge of the World"
Men and Manners: Sketches and Essays (1852)

"On Corporate Bodies"
Table Talk: Essays On Men And Manners http://www.blupete.com/Literature/Essays/TableHazIV.htm (1821-1822)

Source: The Division of Labor in Society (1893), p. 54