If something in you yourself says “you aren’t a painter” — IT’S THEN THAT YOU SHOULD PAINT, old chap, and that voice will be silenced too, but precisely because of that.

Vincent van Gogh (1853-1890) Dutch painter

Letter to Theo van Gogh (28 Oct 1883)
    (Source)

Alt. trans.: "If you hear a voice within you say 'you cannot paint,' then by all means paint, and that voice will be silenced."