Maxims are to the intellect what laws are to actions; they do not enlighten, but they guide and direct; and although themselves blind, are protective. They are like the clue in the labyrinth, or the compass in the night.

[Les maximes sont à l’intelligence ce que les lois sont aux actions : elles n’éclairent pas, mais elles guident, elles dirigent, elles sauvent aveuglément. C’est le fil dans le labyrinthe, la boussole pendant la nuit.]

Joseph Joubert (1754–1824) French moralist, philosopher, essayist, poet

Pensées [Thoughts], ch. 9 “De la Sagesse, de la Vertu, etc. [On Wisdom and Virtue],” ¶ 44 (1850 ed.) [tr. Attwell (1896), ¶ 138]
    (Source)

(Source (French)). Other translations:

Maxims are to the intelligence what laws are to conduct; they do not enlighten, but they guide, they direct, they save us insensibly. It is the thread in the labyrinth, the compass during the night.
[tr. Lyttelton (1899), ch. 8, ¶ 32]

Maxims are to the intelligence what laws are to action: they do not illuminate, but they guide, they control, they rescue blindly. They are the clue in the labyrinth, the ship's compass in the night.
[tr. Collins (1928), ch. 8]