Doctors make mistakes. No-one really likes to admit it or think about it or talk about it, but it happens all the time.
My paternal grandfather was a good case in point. He had gangrene in a leg. They amputated, but not high enough. They told us he would die without a second surgery if they didn’t do a second surgery. They were honest about the odds of him pulling through a second surgery were a million to one. A few years ago, I found a copy of his death certificate online. The primary and secondary causes of death had nothing to do with the surgery or gangrene. They were medical conditions that he had, but they did cause his death.