Review: The central mystery of Nathan Fielder’s new social experiment is Nathan Fielder

Nathan Fielder, whose four-season series “Nathan for You” saw him “aiding” struggling small businesses with strange promotional ideas like poo-flavored frozen yogurt or rebranding a realtor as a “ghost realtor” whose properties are guaranteed to be spook-free, is back. “The Rehearsal,” premiering Friday on HBO, takes off from the idea that critical events can be prepared for, that “if you plan for every variable, a happy outcome doesn’t have to be left to chance.” Like the earlier show, and the myriad reality shows it half-mimics, it is presented as a sort of social experiment, and, in that it puts real people into artificial situations in order to elicit real reactions, even feelings, in some cracked way it