Chance is necessity hidden behind a veil.

[Zufall ist die in Schleier gehüllte Nothwendigkeit.]

Marie von Ebner-Eschenbach (1830-1916) Austrian writer

Aphorisms [Aphorismen], No. 10 (1880) [tr. Scrase/Mieder (1994)]
    (Source)

(Source (German)). Alternate translation:

Accident is veiled necessity.
[tr. Wister (1883)]