“Great commanders never take themselves too seriously.”

Große Männer nehmen sich selbst und die Dinge zu ernst, um öfter als gelegentlich »geistreich« zu sein. Menschen, die nichts sind als eben »geistreich«, sind unfromme Menschen; es sind solche, die, von den Dingen nicht wirklich erfüllt, an ihnen nie ein aufrichtiges und tiefes Interesse nehmen, in denen nicht lang und schwer etwas der Geburt entgegenstrebt. Es ist ihnen nur daran gelegen, daß ihr Gedanke glitzere und funkle wie eine prächtig zugeschliffene Raute, nicht, daß er auch etwas beleuchte! Und das kommt daher, weil ihr Sinnen vor allem die Absicht auf das behält, was die anderen zu eben diesen Gedanken wohl »sagen« werden—eine Rücksicht, die durchaus nicht immer »rücksichtsvoll« ist.
Source: Sex and Character (1903), p. 104.

Of the True Greatness of Kingdoms and Estates
Essays (1625)

No. 407
Characteristics, in the manner of Rochefoucauld's Maxims (1823)

A.V.H. Hartendorp “Don Pañong – Genius" in Philippine Magazine (September 1929).
BALIW

Valedictory Address to medical graduates at Harvard University (10 March 1858), published in The Boston Medical and Surgical Journal Vol. LVIII, No. 8 (25 March 1858), p. 158; this has also been paraphrased "Beware how you take away hope from another human being".
Context: You can never be too cautious in your prognosis, in the view of the great uncertainty of the course of any disease not long watched, and the many unexpected turns it may take.
I think I am not the first to utter the following caution : —
Beware how you take away hope from any human being. Nothing is clearer than that the merciful Creator intends to blind most people as they pass down into the dark valley. Without very good reasons, temporal or spiritual, we should not interfere with his kind arrangements. It is the height of cruelty and the extreme of impertinence to tell your patient he must die, except you are sure that he wishes to know it, or that there is some particular cause for his knowing it. I should be especially unwilling to tell a child that it could not recover; if the theologians think it necessary, let them take the responsibility. God leads it by the hand to the edge of the precipice in happy unconsciousness, and I would not open its eyes to what he wisely conceals.

Introductio ad prudentiam: Part II (1727), Gnomologia (1732)

Ceux qui s'appliquent trop aux petites choses deviennent ordinairement incapables des grandes.
Maxim 41.
Reflections; or Sentences and Moral Maxims (1665–1678)

Source: Moral Man and Immoral Society (1932), pp. 8-9
Context: The inevitable hypocrisy, which is associated with the all the collective activities of the human race, springs chiefly from this source: that individuals have a moral code which makes the actions of collective man an outrage to their conscience. They therefore invent romantic and moral interpretations of the real facts, preferring to obscure rather than reveal the true character of their collective behavior. Sometimes they are as anxious to offer moral justifications for the brutalities from which they suffer as for those which they commit. The fact that the hypocrisy of man's group behavior... expresses itself not only in terms of self-justification but in terms of moral justification of human behavior in general, symbolizes one of the tragedies of the human spirit: its inability to conform its collective life to its individual ideals. As individuals, men believe they ought to love and serve each other and establish justice between each other. As racial, economic and national groups they take for themselves, whatever their power can command.

Source: The Soul of a Butterfly: Reflections on Life's Journey