So how do we do that? Basically three ways
1. Observation from life (hired models, strangers on the bus, your friends)
2. Observation from photo reference (hired models, strangers in books and magazines, your friends).
3. Construction from memory and general principles (Cartoons, Comics, Bridgman, your favorite children’s book etc.) This is easily the most difficult of the three to master, and the arena where a skilled animator or illustrator, will just run circles around someone only trained in the first two methods. I think that’s Dunn’s point anyway. If you know what you’re doing as a cartoonist then you can let your imagination run wild again, like when you were little, except that now your human figures will look halfway decent.
If you want to be truly tight, you probably should try to work with all three, because each method has its own uses, and presents unique challenges that you have to overcome in order to stop sucking at it.