Young Sheldon Retcons Most Annoying Trait To Leonard
CBS' Young Sheldon retcons Sheldon's (Jim Parsons) most annoying trait to Leonard (Johnny Galecki) in The Big Bang Theory.
The prequel sitcom builds on the story of its parent series, with new revelations about the socially-inept genius' childhood in Texas. However, there are also instances where Young Sheldon changes Sheldon's behavior, effectively creating plot holes for the character's overarching story. 
Debuting in 2007, The Big Bang Theory initially only had five main characters - Sheldon, Leonard, Penny (Kaley Cuoco), Howard (Simon Helberg), and Raj (Kunal Nayyar).
Despite being an ensemble sitcom, the show's true lead was always Jim Parson's Sheldon. He was typically the center of narratives, and on the rare occasions where he wasn't, he was still an important player.
Although he dated and eventually married Amy, Sheldon's most important relationship in The Bang Theory was with Leonard, since they'd been together as friends even before the show began.
Viewers had seen Leonard tolerate Sheldon's antics in The Big Bang Theory. Before Amy and Penny were even subjected to his oddities, Leonard was already dealing with him since they're roommates.
Sheldon's penchant for adhering to a strict schedule at home in The Big Bang Theory was particularly difficult for Leonard.