To be content with little is difficult; to be content with much, impossible.

[Sich mit Wenigem begnügen ist schwer, sich mit Vielem begnügen noch schwerer.]

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

Aphorisms [Aphorismen], No. 89 (1880) [tr. Wister (1883)]
    (Source)

(Source (German)). Alternate translation:

To be satisfied with little is hard, to be satisfied with a lot is impossible.
[tr. Scrase/Mieder (1994)]