I have been drawing professionally for about a quarter of a century and it is my experience there are a lot of sequences that recur. A hand is a complex piece of anatomy but you really only need a mental library of a few dozen poses to meet most needs, for instance. You don't repeat it exactly every time, it's easy to change the angle a little, the lighting needs to adapt to the scene, some hands are dainty and some are big meatslabs, but that's all about as easy to adjust on the fly as, say, shifting the rhythm of a rock song you know well into a big band swing groove.

You also learn a discipline we artists call "construction", wherein you can quickly break any object down into a few basic shapes that are incredibly easy to reason about in 3d, and quickly layer details atop that.

Also consider a daily comic strip. How many times do you think Charles Schultz drew Charlie Brown in a single year? How many of those drawings were largely similar to each other? Now that's serious production work. Animation's similar, you probably have a wider range of angles and motion than in a 1970s newspaper comics page but you are still drawing the same character a zillion times and your hand learns stuff and spits it back out without any conscious thought on your part.