“In training a child to activity of thought, above all things we must beware of what I will call "inert ideas"—that is to say, ideas that are merely received into the mind without being utilised, or tested, or thrown into fresh combinations.
In the history of education, the most striking phenomenon is that schools of learning, which at one epoch are alive with a ferment of genius, in a succeeding generation exhibit merely pedantry and routine. The reason is, that they are overladen with inert ideas. Education with inert ideas is not only useless: it is, above all things, harmful—Corruptio optimi, pessima”

1920s, The Aims of Education (1929)

Variant: The only thing worse than being sad is for others to know you are sad.
Source: Everything Is Illuminated

Metaphysics, again, is the Dynamics of Thought; treats of the primary Powers of Thought; occupies itself with the mere Soul of the Science of Thinking. Metaphysical ideas stand related to one another, like thoughts without words. Men often wondered at the stubborn Incompletibility of these two Sciences; each followed its own business by itself; there was a want everywhere, nothing would suit rightly with either. From the very first, attempts were made to unite them, as everything about them indicated relationship; but every attempt failed; the one or the other Science still suffered in these attempts, and lost its essential character. We had to abide by metaphysical Logic, and logical Metaphysic, but neither of them was as it should be.
Pupils at Sais (1799)

22 : The treasure of ki testing
Ki Sayings (2003)

Part 4, section 1.
The Cunning Man (1994)

285e-286b
Statesman

The Law of Mind (1892)

Interview with Conrad Bodman, curator at the Barbican Arts Centre (2001)
Context: Ideas must be put to the test. That's why we make things, otherwise they would be no more than ideas. There is often a huge difference between an idea and its realisation. I've had what I thought were great ideas that just didn't work. Sometimes it's difficult to say if something has worked or not. Photography is a way of putting distance between myself and the work which sometimes helps me to see more clearly what it is that I have made.

22 : The treasure of ki testing
Ki Sayings (2003)