Suppose that you see someone on another boat making a mistake. It is an unwritten rule of etiquette that we have learned about conversations with captains. It is OK to offer help, but it is not OK to offer unsolicited advice on how the captain should operate his vessel.
I'm sure that other experienced sailors will disagree with me. They would impulsively shout out anything they thought helpful. I'm also sure that many captains would deeply resent that kind of unsolicited advice even if if you don't hear them yell back, "F*** Off"
On one hand, it seems like a peculiar rule. If you see a plain mistake or think that you can be helpful, why not speak up? Let me change the context slightly. Suppose a passenger on an airplane tried to point out to the pilot that he was flying the plane incorrectly? In that context, you'll probably agree that it is not peculiar that the passenger risks getting ejected from the plane.
The most common exigent circumstance when this rule comes up is when a vessel approaches a dock. There are often numerous people on shore shouting "do this" "do that". It took me a long time to train Libby to shut her ears to that advice and to focus on doing what the captain said.
But sometimes those other people on shore are right and the captain is wrong. That's true. I recall several times when I was wrong. Nevertheless, a crew must act as a team. They can only do that when they follow the orders of the captain on a vessel or the calls of the quarterback in football.
There may be one member of the crew, such as the co-pilot on a plane, whose job it is to call attention to mistakes, but that privileged relationship must be established in advance.
Therefore, there is wisdom in the rule that the crew follows the captains orders right-or-wrong, and that non-crew should never offer unsolicited advice to the captain while he is engaged in operating the vessel.