“Cultivate that kind of knowledge which enables us to discover for ourselves in case of need that which others have to read or be told of.”

Source: Better-World Philosophy: A Sociological Synthesis (1899), Egoism and Altruism, pp. 117–118

Peace and the Public Mind (1935)

Source: My Inventions (1919)
Context: He declared that it could not be done and did me the honor of delivering a lecture on the subject, at the conclusion he remarked, "Mr. Tesla may accomplish great things, but he certainly will never do this. It would be equivalent to converting a steadily pulling force, like that of gravity into a rotary effort. It is a perpetual motion scheme, an impossible idea." But instinct is something which transcends knowledge. We have, undoubtedly, certain finer fibers that enable us to perceive truths when logical deduction, or any other willful effort of the brain, is futile.

Page 14.
A Grammar of the English Language (1818)

Source: Reason: The Only Oracle Of Man (1784), Ch. V Section II - Containing Observations on the Providence and Agency of God, as it Respects the Natural and Moral World, with Strictures on Revelation in General

1960s, Freedom From The Known (1969)
Context: For centuries we have been spoon-fed by our teachers, by our authorities, by our books, our saints. We say, "Tell me all about it — what lies beyond the hills and the mountains and the earth?" and we are satisfied with their descriptions, which means that we live on words and our life is shallow and empty. We are secondhand people. We have lived on what we have been told, either guided by our inclinations, our tendencies, or compelled to accept by circumstances and environment. We are the result of all kinds of influences and there is nothing new in us, nothing that we have discovered for ourselves; nothing original, pristine, clear.

Gorgias

Opera Omnia, ser. 1, vol. 2, p. 459 Spcimen de usu observationum in mathesi pura, as quoted by George Pólya, Induction and Analogy in Mathematics Vol. 1, Mathematics and Plausible Reasoning (1954)
Context: It will seem a little paradoxical to ascribe a great importance to observations even in that part of the mathematical sciences which is usually called Pure Mathematics, since the current opinion is that observations are restricted to physical objects that make impression on the senses. As we must refer the numbers to the pure intellect alone, we can hardly understand how observations and quasi-experiments can be of use in investigating the nature of numbers. Yet, in fact, as I shall show here with very good reasons, the properties of the numbers known today have been mostly discovered by observation, and discovered long before their truth has been confirmed by rigid demonstrations. There are many properties of the numbers with which we are well acquainted, but which we are not yet able to prove; only observations have led us to their knowledge. Hence we see that in the theory of numbers, which is still very imperfect, we can place our highest hopes in observations; they will lead us continually to new properties which we shall endeavor to prove afterwards. The kind of knowledge which is supported only by observations and is not yet proved must be carefully distinguished from the truth; it is gained by induction, as we usually say. Yet we have seen cases in which mere induction led to error. Therefore, we should take great care not to accept as true such properties of the numbers which we have discovered by observation and which are supported by induction alone. Indeed, we should use such discovery as an opportunity to investigate more exactly the properties discovered and to prove or disprove them; in both cases we may learn something useful.

On ne reçoit pas la sagesse, il faut la découvrir soi-même après un trajet que personne ne peut faire pour nous, ne peut nous épargner.
Source: In Search of Lost Time, Remembrance of Things Past (1913-1927), Vol II: Within a Budding Grove (1919), Ch. IV: "Seascape, with a Frieze of Girls"