[blt]

You conflate geometry and topology * . The topology of the human hand is right in front of you to examine. A lettuce leaf is like a disk plus a wavy boundary and noise. Broccoli is a tree. A bicycle is topologically complex object with high genus. A bad drawing of a hand can still has the right connectivity, it could be smoothly deformed into a realistic hand. Not true for most of these bicycle drawings.

* using "topology" to refer to the graph structure of the skeleton of the solid, not the typical mathematical meaning.

[Doxin]

> it could be smoothly deformed into a realistic hand.

It's probably a good thing that this isn't what defines a drawing as good. A bicycle frame has a couple straight lines and that's about it. A hand, or broccoli, has complex compound curves all over the place.

Ask any artist to draw a bicycle and it'll probably end up pretty good. Ask any artist to draw a hand and there's a good chance it'll not end up good, even when using reference material.

There's a reason a lot of artists have problems drawing hands.

[gowld]

Hands aren't hard to draw because hands are super complicated; hands are hard to draw because humans are evolutionarily finely tuned to recognize and be disgusted by distorted human bodies, which in nature is a signal of disease. Look at the diversity of broccoli proportion at the grocery, then imagine hands with the same diversity -- grotesquely long or lumpy or twisted, which too few or too many fingers. OTOH, cartoon hands, outside the uncanny valley, look fine, even when (as is common) missing a finger.

[logfromblammo]

They just need to pull the Escher trick and draw a hand that can draw hands.

[prince005]

That maybe because hands have a dynamic form/shape while a bicycle has a static form and is thus easier to remember or draw.