... But Letterman’s boredom—his reticence or, on a good day, his guarded enthusiasm—is the secret to his comedy. In fact, it’s been his main theme for more than thirty years. When Bill Murray appeared on the première episode of “Late Night,” in 1982, Letterman prefaced his first question by saying, “This may not be of interest to anybody, and it’s barely interesting to me.” In 1995, when Drew Barrymore, who’d just celebrated her twentieth birthday, claimed to find birthdays depressing, Letterman was all too ready to ask, “Why? Because it signifies the passing of time? Some kind of pointless existence?” In the eighties, Letterman staged elevator races at 30 Rock, where “Late Night” was filmed. The runners, charged with “racing” in their elevators from the sixth floor to the lobby, gathered at the starting line, dashed out of the studio to jab at the buttons, and then waited, while Bob Costas filled the time with play-by-play (“David, the atmosphere down here is incredibly tense”). Sometimes, the races would go on for so long that Letterman would move right into a guest interview. If the guest was boring, it was hard to miss the parallelism.