The adorable team of nerdy scientists on The Big Bang Theory delighted fans for 12 years as they struggled to engage with people outside of academia. What starts out as a tale of a physicist wanting to fall in love with his lovely next-door neighbor quickly develops into a number of amusing narratives with each character facing different challenges in regards to love, family, and the quest for happiness.

By the last episode, Sheldon, Leonard, Howard, Raj, Amy, Bernadette, and Penny have all undergone significant character arcs that have left them significantly different from how they each began the series. This naturally leads to a great deal of misunderstanding among casual viewers—and even devoted fans who only watch reruns—about why their favorite characters behave in particular ways at various periods throughout the series. Here are our answers for some of The Big Bang Theory’s most perplexing scenes in light of this.

Why does Leonard put up with Sheldon’s annoying behavior for so many years?

Even though it’s entertaining to see Sheldon Cooper harass Leonard Hofstadter in their shared flat, living with Sheldon would make anyone nuts. Leonard is required to drive Sheldon everywhere, and the “Roommate Agreement” signs before moving in even details where he can stand in the lavatory. On his couch, Sheldon won’t allow anyone else to occupy his favorite seat. And when ordering takeaway, he makes Leonard follow absurdly detailed instructions.

Sheldon may be Leonard’s friend, but why would anyone want to live in such circumstances? When Leonard Hofstadter’s mother Beverly Hofstadter pays a visit and exposes that she is just as rigid and self-centered as Sheldon, the season 2 episode “The Maternal Capacitance” provides a hint. Beverly even asks that Leonard make her tea according to the same exacting standards Sheldon uses for his takeaway. This demonstrates why Leonard permits Sheldon to treat him in this manner because he was raised with these conditions to submit to irrational demands.

Later on, though, Leonard says he tolerates Sheldon as well since he thinks Sheldon needs his assistance and the two genuinely enjoy each other. And he’s right; even if Sheldon may be brighter than Leonard, he still needs Leonard to help him get by in social situations and avoid problems. Although living with Sheldon ensures Leonard will always be needed, their relationship may not always be healthy.’

Why does Amy develop such a huge crush on Penny?

In the episode “The Robotic Manipulation,” Amy Farrah Fowler first encounters Penny and treats her with contempt, asking her not to refer to their relationship as “Shamy,” and humiliates Penny by candidly discussing her sex life. But as time goes on, Amy constantly compliments Penny on how beautiful she is, insists that they are best friends, and, in the season 5 episode “The Rothman Disintegration,” famously presents her with a huge painting of the two of them.

Given how disrespectful Amy was to Penny at first, her “girl crush” appears out of nowhere. Apparently, Amy has provided some hints of this, particularly when she notes that an earlier version of the Penny/Amy artwork was created with both of them in the nude. Some viewers assume this suggests Amy has bisexual tendencies.

Fans find that Amy was a very lonesome girl who never had any friends from pre-school all the way through graduate school as Amy shares more about her background. She finally gets the chance to be one of the “cool kids” by joining Penny’s circle, but because she’s socially uncomfortable and wants friends, she probably goes too far.

Why does Sheldon offer to have sex with Amy?

In the early years of their partnership, Sheldon and Amy’s love life (or lack thereof) is a continual source of humor. Amy says she wants to be tactile with Sheldon, but her boyfriend, who appears to be asexual, says he doesn’t want to have “coitus.” Therefore, it is a significant shocker in season 9 when Sheldon proposes having sex with Amy on her birthday in “The Opening Night Excitation.” Sheldon even skips The Force Awakens premiere in favor of spending the night with Amy, which represents a significant change in his persona.

However, this was a long time coming for “Shamy” lovers. Sheldon can be intimate, the television show frequently shows, he just requires more time to get used to the concept. Sheldon’s gradual adaptation to holding hands with Amy and cuddling can be seen in earlier episodes. In “The Agreement Dissection,” she gives him a kiss, which he finds “fascinating” and goes on to initiate kisses himself.

The Cooper/Kripke Inversion, a season 6 episode, contains the best foreshadowing, nevertheless. When asked directly by Penny if he’ll ever sleep with Amy, Sheldon acknowledges that he’s become sufficiently at ease with her that a sexual experience is “a possibility.” The expression on Amy’s face when their date was over proved that the wait had been worthwhile.

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Why does Bernadette develop such a mean streak?

Bernadette Rostenkowski, a microbiologist, seems like a really kind girl until Howard Wolowitz starts dating her. Bernadette seems to be the ideal example of a subdued, kind-hearted partner with her high-pitched voice, short size, and geeky spectacles.

Fans quickly discover Bernadette has a lot of drawbacks, though. When she and Leonard are partnered up for a scavenger hunt, she verbally criticizes Leonard to make him work more quickly because she is a tremendously competitive gamer. Howard is humiliated by her by being told that she earns more money than he does. She is such a bully at work that her coworkers use the handicapped restroom for her personal use just to keep her happy.

Multiple episodes suggest Bernadette has a significant complex over her height and feels she isn’t taken seriously because of her waifish appearance, which helps to explain these seemingly contradicting personality qualities. She consequently develops an excessively confrontational attitude in order to get her way. Unfortunately, Bernadette is one of the meaner characters on the show since she frequently intimidates, lies to, and manipulates others in order to get her way.

Why doesn’t Howard have a Ph.D.?

Howard doesn’t have a Ph.D., in contrast to the majority of the other characters on the show. Howard, a graduate of MIT, joined the Department of Applied Physics at Caltech as an aerospace engineer after earning a Master’s degree there. As opposed to physicists, engineers do not require doctorates, so Howard has no real motivation to pursue higher study.

Unfortunately, Sheldon constantly makes fun of Howard because he doesn’t have a Ph.D. since he thinks he’s less educated than (and hence not as brilliant as) his friends. As an engineer, Howard frequently notes, he gets to create the devices that his buddies can only imagine. His engineering knowledge even enables him to travel to the International Space Station during the season as a Payload Specialist.

Even yet, Howard eventually becomes frustrated with being teased for not having a Ph.D., and in the season 8 episode “The Junior Professor Solution,” he enrolls in a graduate course with Sheldon to begin working towards one (only to drop out when he realizes he can’t stomach Sheldon’s condescending teaching style). Notably, Howard is already intelligent enough to accurately respond to questions at the doctoral level and probably just desires a Ph.D. because he feels insecure around individuals who have doctorates (and who are married to them).

Why does Raj sabotage so many of his relationships?

While Sheldon, Howard, and Leonard are all uncomfortable around women, Rajesh “Raj” Koothrappali raises the bar for social ineptitude considerably. Early on, Raj stops speaking to women and needs alcohol just to interact with them. However, this causes even more issues because “drunk Raj” can be even more annoying and domineering than usual.

By season 6, Raj develops a romantic relationship with the similarly shy Lucy and learns how to approach ladies while sober. Raj is now able to have a committed relationship, although he still struggles in most of his other relationships. Raj chooses to go through with an arranged marriage to a woman named Anu in the final season, but even this arrangement falls through, leaving Raj the only unmarried member of the group at the conclusion of the series.

Even though it sounds unfair, Raj has always had high expectations for the people he interacts with. Raj enjoys romantic films and longs for an improbable romance similar to that in Notting Hill or The Princess Bride. As evidenced in season 9 when he breaks up with his girlfriend Emily Sweeney to chase a lady he recently met (with whom they later break up), this motivates him to leave satisfying relationships in search of something better. Despite this, Raj discovers at the conclusion of the program that he has friends who genuinely care about him, especially Howard, who thinks Raj will finally find a compatible woman.

How did Stuart manage to get into a long-term relationship?

Early in the program, Stuart Bloom, the owner of a comic shop, has a significant personality change. In season 2, Stuart charmingly invites Penny out on a date while also having fun with her. But soon after, he starts to feel insecure, unhappy, and bad with women; these characteristics serve to primarily define his persona for the rest of the play. Debbie Wolowitz, Howard’s obese and unseen mother, whom he looks after until her demise in season 8, appears to be Stuart’s only nice interaction with a woman at one point.

But by season 11, Howard has hired Denise, a gorgeous co-manager, who thinks he’s “hot” because he correctly answered multiple Star Wars trivia questions at Sheldon and Amy’s wedding. The two start dating and develop a committed union that not even Stuart’s last-remaining insecurities can sabotage.

Denise, despite her brief appearance on the show, symbolizes a group of female comic book lovers that is notably underrepresented on The Big Bang Theory. She supports Stuart’s interests and makes him feel good about himself because she too appreciates pop culture and superheroes. Although a side joke in “The Citation Negation” implies that she is drawn to Stuart’s unattractive physique since her parents ran a funeral parlor, it is more likely that their relationship works because of how well-suited their personalities are to one another.

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Why is Penny suddenly okay with becoming a mother?

Penny acknowledges that she has no desire to have children after marrying Leonard. Due to the tension, this causes with her husband, Leonard even contemplates lending his sperm to another marriage in order to become a parent. In the end, he decides to be pleased with the life he is creating with Penny and realizes that he doesn’t want a child he can’t nurture.

But Penny admits she’s pregnant in the series finale, and she suddenly seems eager to become a mother. Executive producer Steve Molaro revealed that Penny’s pregnancy is a reference to a statement Leonard makes in the pilot episode that their children will be “smart and beautiful.” This solely considers Leonard’s emotions, therefore Penny’s sudden wish to become a mother seems out of character.

Penny might have altered her mind about having children after finding out she was pregnant, but it’s also conceivable that she hasn’t given her new circumstance enough thought. In her final encounter, Penny admits to Sheldon that she hasn’t yet told her parents about the pregnancy, indicating that she isn’t entirely at ease with the prospect of being a parent. The series ends before it can be investigated, but this could result in further drama.

How did Howard become such a devoted father and husband?

Howard’s journey on The Big Bang Theory is possibly the most intense of all the character arcs. In season 1, Howard is introduced to the audience as a lecherous womanizer who terrifies girls. However, at the end of the series, he is married to Bernadette and a loving father to two kids.

Although it could appear that Howard has undergone a full transformation, a number of episodes serve to illuminate the reasons behind this development. In season 5, Howard states that he wants to have children and give them the upbringing he was unable to enjoy because his father abandoned him when he was a small child. He may have made rash attempts to acquire a girlfriend out of this desire but without a strong masculine role model

Why did it take so long for the elevator to be fixed?

The lift in Sheldon, Leonard, and Penny’s apartment has been broken since the start of the series. Due to having to climb stairs in almost every episode, the characters are forced to have exposition-heavy dialogues. Although this is a humorous running joke, it does raise the question of how an apartment building could have an inoperable elevator for such a long period of time without breaking a building regulation.

The length of time the lift has been malfunctioning has been accounted for differently in several occurrences. Although he claims the lift broke in 2006 in season 1, Leonard maintains the lift broke in 2003 because Sheldon poured a volatile rocket fuel formula into it, sparing Leonard’s life. The lift is fixed in “The Change Constant,” the season’s penultimate episode, 16 years after it first broke.

This is one plot hole that doesn’t have an easy answer, as it appears absurd that the building’s landlord got no complaints for 16 years (or was miraculously able to escape any legal repercussions for negligence). Even for a sitcom, that sounds like a stretch. Perhaps the block is full of renters who don’t mind getting extra exercise by going up and down stairs.

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