"Jumping the Shark" explained

We've all felt that disconcerting moment when a good TV show goes bad. Whether in the form of an unrealistic plot twist, the unexplained replacement of a key character, or a suspicious drift from the original premise, that palatable drop in quality is what tv critics call "jumping the shark." The term comes from a moment in the series Happy Days when Fonzie literally jumped over a shark wearing water skis. Until then, he was known for his sex appeal and rebellious nature, not sideshow stunts involving aquatic predators. It was a sign of sorry times for the show, but at least it spawned a catchy industry phrase. A second Happy Days shark jump came with its ill-fated spin-off series Joanie Loves Chachi. What were they thinking?