My boss was repairing an equipment breakdown when I approached unnoticed. His eyes were closed. His hands were working to replace a bolt and nut in a location out of eyesight. He startled when I made my presence known because his concentration had been focused on the task. “Don’t you close your eyes too when you work on something you can’t see?” he inquired.
The concept has truth to it. Here’s another application described by the Psalmist David in Psalm 63 written in the wilderness of Judah, likely while fleeing for his life from his own son, Absalom.
“My soul shall be satisfied as with marrow and fatness; and my mouth shall praise thee with joyful lips; when I remember thee upon my bed, and mediate on thee in the night watches.”
This passage led C.H. Spurgeon to comment in The Treasury of David:
“We see best in the dark if we there see God best.”
Barnyard of Heaven 