When does life drawing turn into cartooning?

Got this question on tumblr:
I have a keen interest in cartooning, and am spending quite a bit of time on Gesture drawings, figure drawing, anatomy etc. Is this a good way to go you think? I guess I'm wondering how much knowledge of the realistically drawn figure is necessary to simplify it into a more "cartoon/comic" representation. Is that how you started out? Do you do those kinds of practice? Thanks!!!

Here's my answer:

I actually kind of did the reverse route, going from really stylized and cartoony to try and get more grounded in reality.  My work ALWAYS suffered when I didn’t understand what I was drawing, and it always dramatically improved when I did.  
When artists recommend doing this kind of drawing (gestures, life models, from life sketches, etc), it’s not that it really helps you so far as HOW you draw, except for that practice always helps.  What it does is help with WHAT you draw, which is usually where people with natural draftsmanship ability have the most trouble.  Understanding anatomy, understanding how faces work, understanding gesture, all of that is info that will help immensely when it comes to cartooning.  But translating that understanding to a simplified two-dimensional line based aesthetic is WAY more difficult than we think, because that’s what it is: translation.  You’re actively reinterpreting what you’re seeing into a form that is incredibly far removed from reality, yet still recognizable as the reality it is distorting.  It requires practice and a very specific thought process, on top of all of the physical-act-of-drawing stuff that you also have to contend with.  
We’re extremely lucky, as a society, to grow up in a world full of cartoons.  It makes drawing much more intuitive because we grow up with exposure to that two-dimensional representation (it also limits most kid artists to grow up thinking in line instead of form, which is something I’ve never seen documentation on but feel must be true).  So we do have a leg up here on our ancestors.
My best recommendation when it comes to getting that translation-to-2d down is to study the way that other folks have interpreted it.  A few years ago I found that my faces could not convey as much emotion as I wanted, so I spent a couple of days just doing my best to copy Glen Keane expression guides from Tangled.  In doing so I learned how to use the brow ridge in addition to eyebrows to double or split different emotional depictions, something I couldn’t ever do before (but something that I could understand because I’d studied facial anatomy).  My hands sucked, and so I’ve spent years on them, mostly trying to copy Milt Kahl, but nothing ever stuck.  Finally, I did some screen shots of a background character in the Canadian TV cartoon Little Bear, the first hands I’d ever seen that completely clicked, that were simplified down in a way that I could wrap my head around depicting the anatomy right.  I’ve still got a long way to go, but in studying the breakthroughs of others and really analyzing how they arrive at their final work (and copying the lines they do as practice) you can really help to get past that translation problem.  And once you understand how to depict something, you’re beholden to no one, you can draw from your head and simplify and alter your approach and grow.  But it really, really helps to stand on the shoulders of giants.