“[Servetus] is a wise man who doubtless thought he was teaching the truth, but he fell into the hands of the Devil.. . . Be careful the same thing does not happen to you!”

Epistulae Morales ad Lucilium (Moral Letters to Lucilius), Letter LXXVI: On Learning Wisdom in Old Age

Source: Man and Superman

Quand il veut, le diable fait tout bien.
Le Doyen de Badajoz. (Ed. 1818, Vol. III., p. 266).
Translation reported in Harbottle's Dictionary of quotations French and Italian (1904), p. 185.

Source: Patriotism and Christianity http://en.wikisource.org/wiki/Patriotism_and_Christianity (1896), Ch. 17
Context: One free man will say with truth what he thinks and feels amongst thousands of men who by their acts and words attest exactly the opposite. It would seem that he who sincerely expressed his thought must remain alone, whereas it generally happens that every one else, or the majority at least, have been thinking and feeling the same things but without expressing them.
And that which yesterday was the novel opinion of one man, to-day becomes the general opinion of the majority.
And as soon as this opinion is established, immediately by imperceptible degrees, but beyond power of frustration, the conduct of mankind begins to alter.
Whereas at present, every man, even, if free, asks himself, "What can I do alone against all this ocean of evil and deceit which overwhelms us? Why should I express my opinion? Why indeed possess one? It is better not to reflect on these misty and involved questions. Perhaps these contradictions are an inevitable condition of our existence. And why should I struggle alone with all the evil in the world? Is it not better to go with the stream which carries me along? If anything can be done, it must be done not alone but in company with others."
And leaving the most powerful of weapons — thought and its expression — which move the world, each man employs the weapon of social activity, not noticing that every social activity is based on the very foundations against which he is bound to fight, and that upon entering the social activity which exists in our world every man is obliged, if only in part, to deviate from the truth and to make concessions which destroy the force of the powerful weapon which should assist him in the struggle. It is as if a man, who was given a blade so marvelously keen that it would sever anything, should use its edge for driving in nails.
We all complain of the senseless order of life, which is at variance with our being, and yet we refuse to use the unique and powerful weapon within our hands — the consciousness of truth and its expression; but on the contrary, under the pretext of struggling with evil, we destroy the weapon, and sacrifice it to the exigencies of an imaginary conflict'.

Man a Machine (1747), p. 85

Source: Les Miserables

1880s, Garfield's Words (1882)