“It is not good to settle into a set of opinions. It is a mistake to put forth effort and obtain some understanding and then stop at that.”
Hagakure (c. 1716)
Context: It is not good to settle into a set of opinions. It is a mistake to put forth effort and obtain some understanding and then stop at that. At first putting forth great effort to be sure that you have grasped the basics, then practicing so that they may come to fruition is something that will never stop for your whole lifetime. Do not rely on following the degree of understanding that you have discovered, but simply think, "This is not enough."
One should search throughout his whole life how best to follow the Way. And he should study, setting his mind to work without putting things off. Within this is the Way.
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Tsunetomo Yamamoto 65
Samurai 1659–1719Related quotes

Reflections- The Poetical Works and remains of Henry Kirke White, G. Routledge, London 1835.
Other
Source: A Theory of Justice (1971; 1975; 1999), Chapter IX, Section 87, p. 586
Context: I have tried to set forth a theory that enables us to understand and to assess these feelings about the primacy of justice. Justice as fairness is the outcome: it articulates these opinions and supports their general tendency.

As quoted after his arrest for treason; see Treason: the story of disloyalty and betrayal in American history http://books.google.com/books?id=lXZKAAAAMAAJ&q=%E2%80%9CIf+a+man+isn%27t+willing+to+take+some+risk+for+his+opinions,+either+his+opinions+are+no+good+or+he%27s+no+good%E2%80%9D&dq=%E2%80%9CIf+a+man+isn%27t+willing+to+take+some+risk+for+his+opinions,+either+his+opinions+are+no+good+or+he%27s+no+good%E2%80%9D&hl=en&sa=X&ei=RgacUteRAZDYoATC1IDYCg&ved=0CDcQ6AEwAjgU by Nathaniel Weyl (1950), p. 400

"Civilization," London and Westminster Review (April 1836)
Context: We are not so absurd as to propose that the teacher should not set forth his own opinions as the true ones and exert his utmost powers to exhibit their truth in the strongest light. To abstain from this would be to nourish the worst intellectual habit of all, that of not finding, and not looking for, certainty in any teacher. But the teacher himself should not be held to any creed; nor should the question be whether his own opinions are the true ones, but whether he is well instructed in those of other people, and, in enforcing his own, states the arguments for all conflicting opinions fairly.