Tam Nguyen's (Robert Wu) existence may explain why Sheldon Cooper (Jim Parsons) took Sebastian (Steven Yeun) as his roommate before Leonard Hofstadter (Johnny Galecki) in The Big Bang Theory. Debuting in the second episode of Young Sheldon season 1, titled "Rockets, Communist, and the Dewey Decimal System," Tam - a Vietnamese American boy - became Sheldon's very first friend after meeting him in high school. Sheldon took it upon himself to use techniques from a self-help book to finally make some friends, but to no avail. Meeting Tam, however, was purely coincidental, with the two immediately bonding over their shared struggles of fitting in. Despite getting separated, Tam actually significantly affected Sheldon's life, as he was the one to introduce him to his non-science-related interests like comic books and role-playing games.
As shown in a flashback scene in "The Staircase Implementation" back in season 3, Sheldon's former roommate (who was moving out of the building) cautioned Leonard to "run fast, run far." While it has never been revealed what's the cause of his falling out with Sheldon, it didn't seem like the two had much in common. Considering Sheldon's strict (sometimes to the point of ridiculousness) roommate screening process, it's curious what prompted him to accept Sebastian in the first place. Tam's introduction in the current season of The Big Bang Theory might have answered this mystery.
In the latest episode of The Big Bang Theory season 12 titled The "Tam Turbulence," the gang learned about Sheldon's old high school best friend, whom he has never mentioned, which understandably raised some questions. Obviously this was because the character only debuted last year in Young Sheldon, but in the show Sheldon explained that he hasn't spoken to him for over 20 years due to a falling out just before he moved to California. As it turns out, Tam promised to come with him and become his roommate, but backed out last minute after getting a girlfriend. Sheldon was so hurt by this that he even admitted to Amy that he thought he'd never get new friends after Tam. Sheldon never confronted Tam about this, leaving the latter unaware of his best friend's struggles and thinking that the two can catch-up when he comes to CalTech with his son.
So given this, could it be that it was not a coincidence that Sheldon's previous roommate before Leonard bore a physical resemblance to Tam? It sounds shallow, but given his oddities, it's not outside the realm of possibility that he'll look up to another Asian person (albeit with a different nationality) to become his brand new best friend. In fact, when Tam made his debut in Young Sheldon many were convinced that he was Yeun's character in The Big Bang Theory. However, while he was never named on screen, the former The Walking Dead star was credited as Sebastian, effectively squashing that theory.
Tam's appearance in The Big Bang Theory also further tied Young Sheldon with its parent series. Aside from the Coopers, fans really haven't had the chance to see any other person in Sheldon's life in Texas until now. By the end of the episode, Sheldon and Tam made amends which highlights the former's growth as a person - something that the series has been working on for a couple of seasons now. With the door finally open for more characters from Sheldon's past to emerge, it's curious if CBS has any plans of bringing other players in the spinoff to the long-running sitcom.
The Big Bang Theory airs every Thursday, 8 pm ET on CBS.