Warning! Spoilers ahead for Young Sheldon season 5.
Sheldon's saddest story from The Big Bang Theory has become even more tragic because of Young Sheldon. In the original sitcom, Sheldon (Jim Parsons) came equipped with numerous oddities and quirks that he frequently insisted upon, forcing his friends and family to make concessions. This includes the character having to knock exactly three times every time he enters a room. It was a nuisance at first, but apparently, Sheldon's knocking habit was due to a traumatic incident from his childhood.
In The Big Bang Theory season 10 episode "The Hot Tub Contamination," Sheldon told Penny (Kaley Cuoco) the real reason behind his need to knock three times. He adopted the habit after he accidentally caught his dad having sexual relations with another woman while they were still living together in Texas. One day when he was 13 years old, he unexpectedly came home early from college and barged in on George (Lance Barber) and an unnamed female being intimate. Since then, he decided that knocking three times offered people enough time to make themselves respectable, preventing another similarly awkward incident.
Timeline-wise, Young Sheldon is set up to tackle George’s infidelity and eventual death. But while viewers wait for this to be depicted on the show, the prequel spin-off has already made this experience so much more tragic. In Young Sheldon season 5, episode 8, "The Grand Chancellor and a Den of Sin," Sheldon struggles with the idea that everyone lies. Talking with Mary (Zoe Perry), the Cooper matriarch tells her son that she likes that he's always truthful and that she hopes he never changes. Touched by his mother's encouragement, Sheldon promises never to lie to her, making her happy.
However, the socially-inept genius was never able to keep this oath as he deliberately hid his father's affair from Mary. Based on his story in The Big Bang Theory, after he caught George in a compromising position, they never talked about it. Since Mary never mentioned George’s affair in all of the time she visited her son in Pasadena, it's more than likely that she wasn't aware of this.
While Sheldon liked saying that he has an eidetic memory in the original show, Young Sheldon proves that he isn't exactly a reliable narrator. For starters, Sheldon's description of George in The Big Bang Theory is quite different from the character's depiction in the prequel series. Despite this, his story about George's infidelity is arguably the most anticipated plotline in Young Sheldon. The fact that he never fully discussed it with anyone else until he shared it with Penny could mean that there were lapses in Sheldon’s recollection of the incident.
Perhaps there was a massive misunderstanding and that George wasn't exactly having an affair. The problem is, as long as CBS doesn't offer a definitive version of what happened, fans will always have questions about it. And based on what happened in Young Sheldon season 5, it may have been more traumatizing to him than initially perceived. Considering how frank and truthful he can be, it must've been difficult for Sheldon to keep his worst The Big Bang Theory secret from his mother.