" Depicting veils came naturally to Leonardo. He had a fingertip feel for the elusive nature of reality and the uncertainties of perception. Understanding that light hits multiple points on the retina, he wrote that humans perceive reality as lacking razor-sharp edges and lines; instead, we see everything with a sfumato-like softness of the edges. This is true not only of the misty landscape stretching out to infinity; it applies even to the outlines of Lisa’s fingers that seem so close we think we can touch them. We see everything, Leonardo knew, through a veil. "

― Walter Isaacson , Leonardo da Vinci