It reminds be a bit of working as a director in a theater. You tell the actors what you want, and it's never just a "line reading". That's sort of the equivalent of just drawing it yourself, because you can't -- not just that you lack the expertise, but that you need them to do their thing with their body, and it has to be done their way or it looks fake.

So you end up using language that's sort of reminiscent of that, creating an emotional picture. It usually takes multiple passes to transfer the whole idea from your head to theirs.

I'm told that animation directors end up doing exactly the same thing. A digital model really can do what human actors can't. You could say "make that eyebrow curve 10% more" to an an animator. But it won't work unless you tell them why and what it means.