Comment by nerdponx

It can't be that hard to sketch what you see on a sunny day or in candlelight and start to make sense of the rules, right? Getting perspective to look right in paintings seems like it should be a more challenging invention than how shadows behave around corners, walls, and other objects. Getting the sizes and shapes of the shadows correct would be another matter, however.

So I am willing to assume that if a shadow fails to climb up a wall, it's because the artist thought it looked better without the shadow on the wall.