For Peter Jochems:
Your kind and thoughtful examples proved my point and I thank you so much for posting the Vermeer details.
As you can see, only the Vermeer on the upper left has the shadow on the left eye disconnected. This is a good example that shows how Vermeer understood the principle and made the shadow lighter in that (left) eye socket.
Rules can indeed be broken. But the principle that the rule is based on cannot be broken if one is to paint well.
And yes, I agree, Steven can paint any way he wishes too.