We are stubborn because we are narrow-minded; it is hard to believe what is beyond the scope of our vision.

[La petitesse de l’esprit fait l’opiniâtreté, et nous ne croyons pas aisément ce qui est au delà de ce que nous voyons.]

François VI, duc de La Rochefoucauld (1613-1680) French epigrammatist, memoirist, noble
Réflexions ou sentences et maximes morales [Reflections; or Sentences and Moral Maxims], ¶265 (1665-1678) [tr. Heard (1917), ¶273]
    (Source)

This maxim was in the 1st (1665) edition (with the wording "... fait souvent l’opiniâtreté ...")

(Source (French)). Other translations:

It is from a Weakness and Littleness of Soul, that Men are Stiff and Positive in their Opinions; and we are very loth to Believe, what we are not able to Comprehend, and make out to Our Selves.
[tr. Stanhope (1694), ¶266]

Narrowness of mind is often the cause of obstinacy: we do not easily believe beyond what we see.
[pub. Donaldson (1783), ¶319; ed. Lepoittevin-Lacroix (1797), ¶248]

Narrowness of mind is often the cause of obstinacy; we believe no farther than we can see.
[ed. Carvill (1835), ¶458]

Narrowness of mind is the cause of obstinacy -- we do not easily believe what is beyond our sight.
[ed. Gowens (1851), ¶276]

A narrow mind begets obstinacy, and we do not easily believe what we cannot see.
[tr. Bund/Friswell (1871), ¶265]

Obstinacy of opinion is due to want of intelligence; we find it difficult to believe what is beyond our mental horizon.
[tr. Stevens (1939), ¶265]

A small mind is a stubborn mind; it is hard to believe what lies beyond our field of vision.
[tr. FitzGibbon (1957), ¶265]

A small mind becomes an obstinate mind: we find it hard to believe what lies beyond our understanding.
[tr. Kronenberger (1959), ¶265]

Obstinacy comes from limited intelligence, and we do not readily believe what is beyond our field of vision.
[tr. Tancock (1959), ¶265]

Narrowness of mind begets obstinacy; and we do not easily believe what we cannot see ourselves.
[tr. Whichello (2016) ¶]