Gesture drawing is one of those things you learn about in art school. It's all about capturing the essence of form and movement as simply and quickly as you can. It sneaks past your brain so you don't have time to say "That's not right" or "That's rubbish" or pretty much anything, because by the time you've done that, your subject is gone.
Yesterday I sat on the curb at a local arts festival and watched people walk by, and then attempted to draw them as they passed, which meant I had to work really quickly..
One of the main shapes I encountered was the "lady with big purse" where there was a body shape and then a big bag in front of it...
There were also various kids and small dogs...
And then, of course, bermuda shorts.
Various children needed to be held or carried, too.
Gesture drawing is about catching the basic shape and personality of something, just as you see it. And, when people are walking away, you can't get too picky about finishing it. But it's a terrific way to see better and not get stuck.
You can read more about gesture drawing here, and of course there is the Google. Or, you can just go out and try it. Just bring a lot of paper, you go through it really fast!