Loyalty of two doctors

On the Otzah forum, someone raised the following question, and I would be happy to hear the Rabbi's opinion on this:
The poskim wrote that one does not fear in the protection of life from the opinion of a single doctor against many, but two doctors, even against a hundred doctors, fear the opinion of the two. What is the explanation for this? One does not fear against a few, and two do fear against a hundred?

I also wanted to ask what the law is regarding something that is not a matter of life and death, but only harm to the body. Are there concerns about the minority opinion in this case as well?