To make the obvious explicit in the case of Princess Diana contrasted with the Queen Mother, the reason I say I find modern psychology incomprehensible is that I can quite easily imagine myself behaving as the Queen Mother did, and never giving away anything that the royal family would not consider it to be in their interests to have given away. But I cannot imagine at all the psychological events that went into Diana's very damaging public discussion of Prince Charles, to whom she was married. And yet I suppose a lot of people can imagine this, since such betrayals of confidence appear to go on all the time in modern society, at all social levels, so I suppose that there is no longer any such thing as a concept of something being in confidence between individuals.
From the television dramas one gathers that it is considered interesting and attractive to promise not to give something away, and then to do so, which shows there is an awareness that you do not have to keep your word, although you may have led someone to believe (more fools they) that they can rely on you to do so.
When people do insist on not giving away information about someone, this is virtually always portrayed as misguided. They are covering up for a criminal or pervert in withholding information from police or doctors, setting other people at risk and preventing the criminal or pervert from getting the punishment he deserves or the "help" which he needs.
Cases almost never occur in the television dramas in which an individual is protected by discretion from wrongful persecution by agents of the collective.
I say "almost" never because there was a case recently in which a policeman threw away a cassette which might have incriminated someone. But the "someone" was a doctor, hence "good". The crime of which the doctor might have been convicted was (so far as I could gather from a very inattentive observation of the unattractive episode) that of assisting a suicide in framing someone on whom he wished to take revenge, so that they would be supposed to have murdered him when he was found dead.