In general doctors are fairly competent, but overwork and natural human inattention combined with the absurd power structure that’s historically been cemented into the medical profession (“I’m the doctor, I know best, you’re just the patient and not qualified to know anything about what’s happening to you”) mean that occasionally mistakes do happen.
When my mother was 12 years old she was hit by a bus and dragged along the road for 330 meters before a passer-by waved the bus to a halt and she was eventually extricated. In the hospital they correctly diagnosed a broken right arm and then proceeded to put the (unharmed) left arm in a cast while leaving the right arm unattended. It took two days for someone to listen to my mother and rectify the situation.
What this means is that anyone requiring the services of a physician needs (i) to educate themselves as best as possible on the likely issues and possible treatments, and (ii) push the doctor into the role of consultant rather than all-powerful expert, so that a proper diagnosis and treatment regime can be mutually agreed upon. And any resulting problems should be loudly and persistently broadcast by the person suffering from them until the medical staff pay proper attention and rectify the problem.
Doctors are just people like the rest of us, so we can’t expect them to be perfect.