Caspar David Friedrich — German Artist born on September 05, 1774, died on May 07, 1840

Caspar David Friedrich was a 19th-century German Romantic landscape painter, generally considered the most important German artist of his generation. He is best known for his mid-period allegorical landscapes which typically feature contemplative figures silhouetted against night skies, morning mists, barren trees or Gothic ruins. His primary interest as an artist was the contemplation of nature, and his often symbolic and anti-classical work seeks to convey a subjective, emotional response to the natural world. Friedrich's paintings characteristically set a human presence in diminished perspective amid expansive landscapes, reducing the figures to a scale that, according to the art historian Christopher John Murray, directs "the viewer's gaze towards their metaphysical dimension"... (wikipedia)

The painter should paint not only what he has in front of him, but also what he sees inside himself.
Close your bodily eye, that you may see your picture first with the eye of the spirit. Then bring to light what you have seen in the darkness, that its effect may work back, from without to within.
I have to stay alone in order to fully contemplate and feel nature.
If he sees nothing within, then he should stop painting what is in front of him.