Painters have a troubled relationship with shadows. The artist's studio typically faces north, so that direct light is attenuated.
Shadows are notoriously difficult to paint.
They are extremely salient and can show up as black patches on a painting. Lines and other marks on shadows destroy the shadow character. Fuzziness or the sfumato effect require a skilled hand. Only perfect mastery of perspective can help produce geometrically correct shadows All the same, perceptual tolerance on the viewer's part for wrong shadows is relatively high. This in turn suggests that shadows are processed by the visual system in a relatively loose way.