There are more fools than wise men, and even in the wise there is more folly than wisdom.

[Il y a plus de fous que de sages, et dans le sage même, il y a plus de folie que de sagesse.]

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. 2, ¶ 149 (1795) [tr. Merwin (1969)]
    (Source)

(Source (French)). Alternate translations:

There are more fools than wise men, and even in the wise man himself there is more folly than wisdom.
[tr. Hutchinson (1902)]

There are more fools than wise men, and even in a wise man there is more folly than wisdom.
[tr. Mathers (1926)]

There are more fools than wise people, and in wise people themselves there is more folly than wisdom.
[tr. Siniscalchi (1994)]