Penny suddenly becoming a bartender on season 4 was due to an unfortunate event involving Kaley Cuoco in real life. Before she became a successful pharmaceutical sales representative, the character was an aspiring actress who moved to California from Nebraska. As she struggled to land acting gigs, Penny worked as a waitress at The Cheesecake Factory, before she unexpectedly started manning the restaurant's bar section in The Big Bang Theory season 4.

Unlike the rest of the Pasadena gang, Penny was the only one who wasn't in the scientific field. That makes her more aligned with the viewers' perspective within the show, as Leonard (Johnny Galecki) and Sheldon (Jim Parsons) typically needed to explain to her what they do for a living. For a time, she started feeling insecure about her intellect, and the fact that Sheldon could be mean about it didn't help. While the rest of The Big Bang Theory cast lacked in social skills, she excelled in mingling. Given this, Penny thrived in being a waitstaff at The Cheesecake Factory, despite . So, it was surprising when the establishment suddenly made her a bartender.

The change in Penny's job was motivated by an unfortunate accident. As she recalled in an interview on in 2010, her horse was spooked during a riding lesson and it caused her to fall off of it. When the horse attempted to leap over her, it inadvertently landed on her leg. Cuoco had to miss two episodes of The Big Bang Theory season 4. At the time, the sitcom didn't make a big deal out of it and didn't even explain why she wasn't around. Eventually, during "The Apology Insufficiency" episode, but to hide the actress' leg cast, the writers decided to put her behind the bar at The Cheesecake Factory as its new bartender. Here's her recollection of what exactly happened to her during her riding accident: