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If asked to draw a person's portrait, many people would say “I cannot draw.” Why is observational drawing so hard? In a new paper, @judithfan.bsky.social and I answer: it's the limitations of human vision. Learning to draw is learning skills to overcome them. aaronhertzmann.com/2026/03/23/d... 1/

Drawing is a creative activity, accessible to everyone: all you need is a pen or pencil and paper, and people have been drawing for at least 45,000 years. Psychologists have extensively studied drawing for decades, but no coherent theory for the process of observational drawing has emerged. 2/

One might think that an artist draws a picture by looking at the world, forming a mental picture of it, and then drawing from that picture. Drawing errors are perceptual or motor errors. But no one draws this way, because no one actually keeps a complete picture of what they see in their head. 3/

Here's Henri Matisse drawing a portrait of his son. Watch his head and eyes, and how often they look back and forth between his drawing and his son. Why does he look back and forth so frequently—why can't he just draw his son from memory?
And where exactly is he looking? 4/

One clue is that human vision is severely limited, both in terms of what we see at any moment, and how much of it we remember. And, we are *totally unaware* of how much we do not see, until it is pointed out. Suppose you wanted to draw a picture from this photo of a houseplant, 5/

Look at the photo, and then look away. How many branches does the plant have? How many leaves does each branch have? These questions are easy when looking at it, but nearly impossible afterward. Drawing the picture from memory—capturing details of contour or shading—would be mostly making it up. 6/

These visual limitations explain why artists typically move their eyes so frequently. Here’s a person copying a picture, recorded with an eye tracking device. The black rectangle show where the his eyes are looking at any moment. 8/ (Clip from "Capturing Life" by John Tchalenko)

The brain can store very little detail at a time, so you move your eyes back-and-forth to gather information from the source and then put it in the target. It’s like trying to transfer water between two pots using only a leaky teacup. 9/

What happens if you restrict eye movements? Here’s a 30-second "blind drawing" I made, without looking once at the drawing. I took the photo a moment later. The “errors” are typical of blind drawing: individual shapes are accurate, but their proportions and placements are not. 10/