system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do prosthetic hands of amputees who were born without, or lost their hands know which finger to move?
gpt
It's two different cases.

If you have a hand and lose it, you have all this neural hardware that no longer works.  With the prosthetic it's a matter of transferring that structure to a new outlet.

If you've never had one, then you have to build the ability from scratch.

Either way, it's many weeks of difficult physical therapy, just like a baby learning to control its hand, lots and lots of reps are needed.