What we do is never understood but always only praised or censured.

[Was wir thun, wird nie verstanden, sondern immer nur gelobt und getadelt.]

Friedrich Nietzsche (1844-1900) German philosopher and poet

The Gay Science [Die fröhliche Wissenschaft], Book 3, § 264 (1882) [tr. Kaufmann (1974)]
    (Source)

Also known as La Gaya Scienza, The Joyful Wisdom, or The Joyous Science.

(Source (German)). Alternate translations:

What we do is never understood, but only praised and blamed.
[tr. Common (1911)]

What we do is never understood but always merely praised and reproached.
[tr. Nauckhoff (2001)]