Posing
While the shutter lasts an instant, Rembrandt sat in front of himself for hours and days and weeks recording what he saw. He and his sitters experienced many thoughts and those passed across their faces while Rembrandt looked and recorded.
As it turns out, the great photographers coach the thoughts and emotions of the sitter to a crescendo just when the shutter is clicked and a similar effect is captured.
This is much like how a Japanese ink drawing is undertaken after a meditation and a concentration of powers that give each mark of ink weight.
A painter too, especially in abstraction and expressionism, is able to express in a stroke many thoughts and hours and days of ideas.
The mundane too are full of hours and days and weeks of ideas and experiences that are under the surface. Everyday scenes, or even contrived poses are just as fertile as expressive content to color with violence of pigment and texture. In "Group in Front of Yellow Buildings" even the cloud poses in the frame.