Sounds weird but I thought I'd share in case anyone here was like me and was wondering why drawing on a tablet hurts vs drawing the same way but on paper. The big difference is my wrist was sticking more to the plastic of the tablet surface than it did sliding across paper. My wrist wasn't sliding naturally so I was overextending my wrist muscles causing lots of muscle pain, but with a sheet of paper over the tablet there is a lot less friction so my hand can move and slide much easier meaning no pain