In May 2015, Norm Macdonald appeared on the fourth-to-last episode of “Late Show With David Letterman.” He did about six minutes of stand-up comedy, and then choked up when recalling the first time he saw Mr. Letterman perform. Finally, unsuccessfully fighting back tears, he turned toward the host’s desk and told him, “I love you.”

It was a jarring moment from the bone-dry Mr. Macdonald, and it represented a few more seconds of sincerity than you get in the 240 pages of “Based on a True Story,” his often very funny but always very fabulist “memoir.”

The book is most direct, and most convincingly self-loathing, about the job of comedy. “Stand-up comedy is a shabby business, made up of shabby fellows like me who cross the country, stay at shabby hotels, and tell jokes they no longer find funny,” he writes in the introduction. Later he describes the dependable range of reaction from audiences: “They either hate you or they don’t completely hate you.”

Mr. Macdonald has always been a comic’s comic, best loved for his hyper-arch stand-up, which has shades of Steven Wright’s concise wordplay and Andy Kaufman’s straight-faced extended pranks. Those who aren’t comedy nerds know him best from his stint as the host of “Weekend Update” on “Saturday Night Live,” from 1994 to 1997.