Nothing is so firmly believed, as what we least know.

[Qu’il faut sobrement se mêler de juger des ordonnances divines.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 1, ch. 31, “That a Man must not be too hasty in judging of Divine Ordinances” (1580) [tr. Cotton (1686), Hazlitt (1877)]
    (Source)

Alt. trans.:

• "Nothing is so firmly believed, as that which a man knoweth least." [tr. Florio (1603)]
• "Nothing is so firmly believed as what is least known."