And there were never in the world two opinions alike, any more than two hairs or two grains. Their most universal quality is diversity.

[Et ne fut jamais au monde, deux opinions pareilles, non plus que deux poils, ou deux grains. Leur plus universelle qualité, c’est la diversité.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 2, ch. 37 (2.37), “Of the Resemblance of Children to Their Fathers [De la ressemblance des enfans aux peres] (1579) [tr. Frame (1943)]
    (Source)

Appeared in the first (1580) edition, with revisions in succeeding editions. The specific mention of hairs and grains first appears in the 1595 edition.

(Source (French)). Alternate translations:

And never were there two opinions in the world alike, no more than two haires, or two graines. Diversitie is the most universall qualitie.
[tr. Florio (1603)]

There never were in the world two opinions more alike, than two hairs, or two grains; their most universal quality is diversity.
[tr. Cotton (1686)]

And there never were, in the world, two opinions alike, no more than two hairs, or two grains: their most universal quality is diversity.
[tr. Cotton/Hazlitt (1877)]

And there were never in the world two opinions alike, any more than two hairs or two seeds. Their most universal quality is diversity.
[tr. Ives (1925)]

In the whole world there has never been two identical opinions, any more than two identical hairs or seeds. Their most universal characteristic is diversity. [tr. Screech (1987)]