I know that feeling... I think it is more common than we think. On the other hand, there are some people who have absolutely no problem interjecting their opinion regardless of whether it is wanted or not...
I'm sorry to hear about your friend... medical operations and surgeries are difficult and tricky things at the best of times. There are so many complicating factors... and even the ones with the best chances can go horribly wrong. My brother is a doctor... and they can also get completely blind-sided by something that they would have thought to be routine... in the end, a risk estimate is only a guessed probability... and like all probabilities... you might just get unlucky.
Life certainly is a crap shoot. Being a doctor certainly carries a lot of responsibility and they can’t save everyone but can only do their best.