The surprising surprises once; but the admirable is admired more and more.

[Ce qui étonne, étonne une fois; mais ce qui est admirable est de plus en plus admiré.]

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

Pensées [Thoughts], ch. 23 “Des Qualités de l’Écrivain [Of the Qualities of Writers]” ¶ 164 (1850 ed.) [tr. Lyttelton (1899), ch. 22, ¶ 77]
    (Source)

(Source (French)). Alternate translations:

What astonishes astonishes once, but what is admirable is more and more admired.
[tr. Calvert (1866), ch. 15]

That which astonishes, astonishes once; but whatever is admirable becomes more and more admired.
[tr. Attwell (1896), ¶ 370]

The surprising astonishes once; but the admirable is admired more and more.
[tr. Collins (1928), ch. 22]