And medical incompetence by staff, not doctors, is also awful. My brother hated reading. He got glasses, still hated reading, my mother wondered why he could be so disobedient in that regard. They said, well, the prescription is right, he can clearly see fine. Turns out two years later that the lenses were installed on opposite sides. Right lens on left eye, left lens on right eye. A simple mistake, but the consequences...
I once proved that my wife got the wrong prescription by just holding her old and new glasses up at arms length and seeing that things looked way different through them. The glasses place agreed.
When you get a car engine rebuilt, do they just diagnose, replace parts and then never start the engine themselves to verify it actually works?