I mean, you take one look at Greek statues and Roman busts and you realize that people figured how to aim for realism, at least when it came to the human body and faces, over 2000 years ago.
Yet, unlike sculpture, paintings and drawings remained, uh, “immature” for centuries afterwards (to my limited knowledge, it was the Italian Renaissance that started making realistic paintings). Why?
Close one eye or put an eyepatch on. I’d expect this makes 3D -> 2D transformations easier after a while.
It does, however it doesn’t remove human error and it doesn’t help at all with situations or angles where you don’t have clearly defined contours, such as when representing facial features for example. People tend to draw what they understand, not what they see, even when using the one eye trick.
That is one of the techniques I was taught in a sketching class.