There’s a special sense called proprioception, which is basically “where are all of my movable parts right now.” Your brain uses information from a couple sources, but especially from special sensors in your joints, to know where stuff is. Think of yourself as a stick figure drawing: If your brain knows the angle and twist of your shoulder/elbow/wrist/each knuckle, then it can figure out where your upper arm/lower arm/hand/finger must be. This is very useful information to help with movement even when you’re not looking, so the brain really needs to know.
You don’t have these position sensors in your internal organs, because it wouldn’t help anything. Your liver and kidneys aren’t movable parts; they’re tacked down so, they don’t move relative to the rest of you. Your intestines slip around sometimes, but that’s not really useful information for your brain (which already has a LOT of sensory input to deal with.)
TL;DR: Special position sensors, because hand position matters and liver position doesn’t.
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