In great actions men show themselves as they ought to be, in small actions as they are.

[Dans les grandes choses, les hommes se montrent comme il leur convient de se montrer; dans les petites, ils se montrent comme ils sont.]

Nicolas Chamfort (1741-1794) French writer, epigrammist (b. Nicolas-Sébastien Roch)

Products of Perfected Civilization [Produits de la Civilisation Perfectionée], Part 1 “Maxims and Thoughts [Maximes et Pensées],” ch. 1, ¶ 52 (1795) [tr. Hutchinson (1902), “The Cynic’s Breviary”]
    (Source)

(Source (French)). Alternate translations:

In great matters men show themselves as they ought; in little, as they are.
[tr. Mathers (1926)]

In affairs of importance, men show themselves at their best advantage; in small matters they are seen as they are.
[tr. Merwin (1969)]

In great things, men show themselves as they want to be seen; and in little ones they show themselves as they are.
[tr. Siniscalchi (1994)]

In important matters, men display themselves as they want to be seen; in minor matters as they really are.
[tr. Parmée (2003), ¶45]