Every man hears only what he understands.

[Es hört doch jeder nur, was er versteht.]

Johann Wolfgang von Goethe (1749-1832) German poet, statesman, scientist

Sprüche in Prosa: Maximen und Reflexionen [Proverbs in Prose: Maxims and Reflections] (1833) [tr. Saunders (1893), “Life and Character,” #383]
    (Source)

Posthumous, on "Literature and Life." (Source (German)). Alternate translations:

A man hears only that which he understands.
[tr. Rönnfeldt (1900)]

For surely everyone only hears what he understands.
[tr. Stopp (1995), "Posthumous," #887]