The Simpsons has found a lot of strong drama in the relationship between Bart and Lisa, with their sibling rivalry being at the forefront of plenty of episodes. Despite their familial bonds, the two are often shown bickering, insulting each other or genuinely fighting. Bart's destructive pranks and Lisa's overeager nerdiness often aggravate each other to a ridiculous level.
Over the years, the two have actively worked against each other in various episodes -- only for most episodes to end with Bart and Lisa making peace with one another and reaffirming their connection. But ultimately, many of Bart's genuine problems seem to stem from his sister -- and she rarely faces any real repercussions for this.
The problem is that across the course of The Simpsons, Lisa ends up imparting far more lasting damage to Bart without ever realizing it. The show has spent time delving into what it's like to be in the shadow of a sibling -- and while Bart is always portrayed as more effortlessly charming and popular, Lisa's achievements quickly overshadow his role as a class clown. In numerous episodes -- such as Season 9's "Lisa's Sax" -- it's established that Lisa's startling intelligence and musical skills began to show up in her early years. In the process, however, Bart increasingly got overshadowed. His own dour emotional state went on largely unnoticed by his family, and his decision to become a class clown was treated as a way for him to get the attention that his family wasn't paying him.
While this isn't Lisa's fault -- especially in those early years -- it is something that helped mold Bart into the attention-starved troublemaker. But as the two got older, Lisa is shown repeatedly and actively overshadowing Bart in various ways -- quickly picking up hockey (in Season 6's "Lisa on Ice") and cool aesthetics (like in Season 7's "Summer of 4 Ft. 2") when she wants. In these episodes, Bart's anger is treated as a failing on his part, and he eventually has to overcome his jealousy. But in other episodes, Lisa's jealousy over Bart's innate artistic endeavors (like his quick talent at jazz in Season 18's "Jazzy and the Pussycats") she doesn't go through a similar arc -- and even when she ends up literally injuring Bart, it's ultimately Bart who has to make the amends to Lisa for making her sad.
It even extends to their future lives, with Season 27's "Barthood" highlighting how their rivalry continued into their young adult years. As Bart grew into a teenager, his jealousy over Lisa -- who increasingly became accepted and embraced by the rest of Springfield -- escalated to the point where the pair got into a very vocal argument in front of their friends at Milhouse's high school graduation party. Many of Bart's actual problems across his life have stemmed from these jealousies, even if Bart eventually translated that jealousy into an artistic future that, as other episodes have hinted, is doomed for failure.
Bart and Lisa's series-long rivalry may not have been their fault, and when the pair work as a team they're almost unstoppable as a surprisingly effective mystery-solving duo. But many of Bart's problems have been shown to stem directly from how the world treats him and his sister differently -- and even when Lisa specifically ruins his time, she isn't treated as the antagonist of his story. It adds a tragic layer to Bart's arc in The Simpsons, as his genuine potential is always hinted at but ultimately brushed away in comparison to his far more accomplished and appreciated sister -- even as the future hints at distinctly important futures for both of them.