Thoughts are the shadows of our feelings — always darker, emptier, and simpler.

[Gedanken sind die Schatten unserer Empfindungen, — immer dunkler, leerer, einfacher, als diese.]

Friedrich Nietzsche (1844-1900) German philosopher and poet

The Gay Science [Die fröhliche Wissenschaft], Book 3, § 179 (1882) [tr. Kaufmann (1974)]
    (Source)

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

(Source (German)). Alternate translations:

Thoughts are the shadows of our sentiments -- always, however, obscurer, emptier, and simpler.
[tr. Common (1911)]

Thoughts are the shadows of our sensations -- always darker, emptier, simpler.
[tr. Nauckhoff (2001)]

Thoughts are shadows of our feelings -- always darker, emptier and simpler than these.
[tr. Hill (2018)]