Young Sheldon Reveals Why Big Bang Theory's Weirdest Relationship Makes Sense

"Young Sheldon" fleshes out many of the storylines previously established on "The Big Bang Theory." The prequel sitcom provides insight into Sheldon's (Iain Armitage) early life and explains how childhood events affect him as an adult. As fans of both series know, Adult Sheldon (Jim Parsons) often speaks about his family quite negatively; the depiction of his father, George Sr. (Lance Barber), for example, has been softened a lot on "Young Sheldon." The character is actually a lot closer with his family during his childhood than he would have you believe on the original show. His strong bond with family members, his twin sister Missy (Raegan Revord) in particular, also explains why the weirdest relationship on "The Big Bang Theory" — the one between Sheldon and Penny (Kaley Cuoco) — makes a lot of sense.

Although Sheldon and Missy mock and rib each other as siblings do, they are very close. While they become less involved in each other's lives as the show progresses, they continue to share family dinners and be there for each other to talk through any problems. Oftentimes, Sheldon leans on Missy more than she does on him. This happens with Penny too. Despite their differences, Sheldon and Penny quickly form a strong friendship on "The Big Bang Theory," with the scientist often turning to his neighbor for advice and help navigating social situations.

As fans of both shows may have observed, the characters Missy and Penny are very similar. So, by understanding Sheldon's relationship with his twin, it's much less surprising that he forms such a close bond with Penny on "The Big Bang Theory."

Sheldon's relationship with Penny on "The Big Bang Theory" might seem strange given that he generally associates himself with scientists and academics. However, seeing his relationship with his twin sister on "Young Sheldon" explains a lot, as Missy and Penny have very similar personality traits. Both characters are presented similarly on their respective shows, and may initially be perceived as ditzy and less academically intelligent, but neither of them are stupid by any stretch. They're both kind, empathetic, and emotionally intelligent people. It's really not surprising that they get on so well when adult Missy (Courtney Henggeler) visits Sheldon in California in Season 1, Episode 15 of "The Big Bang Theory." While it may be a subconscious act, Sheldon clearly gravitates toward Penny because he senses these similarities.

Missy shows off her kind and caring side time and time again on "Young Sheldon" and despite her sassy disposition, she always has comforting words for her brother when he needs it. For example, in Season 4, she helps him overcome his fear of graduating high school. To return that affection, Sheldon dedicates his valedictorian speech to her. 

Similarly, Penny's kindness and emotional intelligence are demonstrated in spades on "The Big Bang Theory." She's always patient and understanding in her interactions with Sheldon, and regardless of what's going on with her relationship with Leonard (Johnny Galecki), Penny always maintains their friendship, which gradually evolves into more of a familial bond. It becomes clear how strong that bond is in Season 2, Episode 13. When Sheldon refuses to kick Penny out of his friend group to make room for Barry Kripke (John Ross Bowie), he confirms that she's not simply someone he tolerates in his life but a friend he's come to appreciate.

Alongside having similar personality traits, Missy and Penny help Sheldon navigate certain social situations and big life moments. Sheldon needs his sister a lot more than he'd like to admit. This is evident in Season 5, Episode 4  of "Young Sheldon," when he struggles with Missy moving into her own room. To maintain their connection, he designs a device that knocks loudly on the wall and communicates with her via a walkie-talkie. Sadly, as he grows up, he loses this closeness with Missy, but it seems his friendship with Penny helps fill that sibling void. Eventually, she becomes one of the people he leans on most. However, their friendship didn't have to develop this way; Sheldon is not as close with any of his other friends' partners, and he doesn't bond the same way with any of Leonard's previous girlfriends.

On "The Big Bang Theory," Penny eventually becomes someone Sheldon can trust with his secrets. She's the only person he confides in regarding George's affair, the truth of which fans get to see on "Young Sheldon," and he often turns to her when he reaches a milestone or takes a big step in his relationship with Amy (Mayim Bialik). However, their friendship isn't a one-way street.

In turn, Sheldon helps Penny where he can — he loans her money to pay her rent in Season 2, Episode 14, works with her to make her Penny Blossoms business more effective a few episodes later, and even drives her to the hospital in Season 3, Episode 8, despite not possessing a license. Sheldon also offers a different perspective whenever she has issues in her relationship with Leonard. Ultimately, having Penny as a friend subconsciously encourages Sheldon to care more about the people in his life.