"Trilogy of Error" (known by the individual titles "Homer's Day", "Lisa's Day", and "Bart's Day") is the eighteenth episode of the twelfth season of the American animated television series The Simpsons, and the 266th episode overall. It originally aired on Fox in the United States on April 29, 2001. In the episode, Homer's rush to the hospital to re-attach his severed thumb, Lisa's rush to school to win the science fair, and Bart's run-in with an illegal fireworks scheme are interconnected as each act tells the events of the same day, but from a different point of view.
"Trilogy of Error" was directed by Mike B. Anderson and written by Matt Selman. The episode, initially titled "Go, Simpson Go", was initially pitched by Selman who figured the whole plot out before pitching it. The episode features a guest appearance from Malcolm in the Middle star Frankie Muniz as Thelonious, while Joe Mantegna reprises his role as recurring character Fat Tony.
The episode has received positive reviews since its original airing. Matt Selman named it the best episode he has ever written.