When I was in high school, I had a chance to see the Amazing Kreskin perform his "mind reading" and similar feats in the school gym before a large audience. One of Kreskin's signature stunts is to ask the event organizers to hide his check anywhere in the room where he is performing. If he fails to find it, which apparently hardly ever happens, he forfeits his fee. I still remember watching Kreskin run up and down the risers supposedly drawn by the mental waves he was feeling, until he inevitably found what he was looking for. I can't say for sure how he does it, but it seems likely that in addition to any psychic emanations he might have been picking up, he was reading a lot of highly visible clues from the facial expressions and body language of more than a thousand people in the gym, all of whom knew exactly where the check was hidden.
In mediation, we have two forms of confidentiality, one of which I support, and the other I have some skepticism about, just as I am skeptical of Kreskin's supposed psychic powers. The first confidentiality rule in mediation is that nothing said in the course of a mediation may be quoted in subsequent court proceedings if the case does not settle. There are some questions about the scope of this kind of confidentiality, but in general the rule is easily understood and makes perfect sense. If we want to encourage participants in mediation to be candid about their mistakes and their willingness to make concessions to the other side, we cannot allow adversaries to use those admissions against them in court.
The second kind of confidentiality allows mediators to keep secrets revealed by one side from the other side. Generally, participants in mediation value their ability to engage in what in court would be called ex parte communications with the neutral. Parties like to submit briefs to the mediator labeled CONFIDENTIAL, even when virtually all of the information in those briefs is already known to the other side. They like to share with the mediator the bombshells they intend to drop on the other side if the case goes to trial, and ask the mediator not to make any use of that information. Oftentimes parties actually want the mediator to convey that kind of confidential information to the other side, but to do so in an oblique way, similar to the way the body language of the audience in my high school gym conveyed the location of Kreskin's check to him. Sometimes they want the mediator to be even more direct, by telling the other side something like, "the other side has some information that might be devastating if they use it effectively at trial, but they shared it with me in confidence so I am not allowed to tell you what it is." In that way, the secret trial bombshell might have even more power than if the evidence is revealed.
In any case, people should understand that it's not entirely possible for a mediator who is also a human being to maintain absolutely the confidentiality of information that is conveyed to him ex parte. In fact it is probably next to impossible for a mediator to do that. Poker players all recognize this truth. Even the best of them often show up at tournaments wearing elaborate sunglasses and hats. They understand that their facial expressions and gestures can inadvertently reveal the contents of their hole cards, even while they are trying to keep that information secret. They also deliberately practice deception, otherwise known as the bluff. In mediation, parties and mediators also commit both deliberate deception and unconscious reveals of confidential information. We can convey information with a wink or with a stern face. No matter what expression we assume, we might be sending a false signal, or committing an unknowing tell. If a party authorizes me to convey a particular offer to the other side, but also privately tells me that they can do somewhat better than that offer, I am not going to reveal directly the limits of their authority, but I am probably going to--either deliberately or perhaps inadvertently--convey their offer in a way that suggests that the offer is not final.
In other words, the second type of confidentiality cannot and should not be relied upon entirely. Any mediator who tells you that he will hold information you provide him in strict confidence and will not divulge it to the other side is either fooling you or fooling himself. It's not possible to guarantee that. Moreover, the whole point of revealing confidential information to the mediator is that parties want the mediator to use that information somehow to further the purposes of the mediation, maybe not by repeating it directly, but perhaps by conveying it in a more subtle way. At the very least, parties interested in an evaluative-type mediation are asking the mediator to take confidential information provided by each side into account in determining a value for the case, and they want that evaluation conveyed to both sides. Otherwise, there would be no point in providing confidential information to the mediator in the first place.
Anytime we are withholding information, we are engaged in a form of deception. Whichever of the parties are being deceived--and that usually means both sides--are going to do their best to find out the truth. And generally none of us can help allowing some of that truth to be revealed. That means nobody can entirely trust the mediator, or themselves, to keep from revealing in some manner information that they are supposedly holding in confidence. And generally that is the way parties should want it.