Sheldon Cooper is the point of focus on The Big Bang Theory. Although his best friend and roommate, Leonard, may be the nucleus of their friend group, it's because of Sheldon's quirks that the gang does what they do. In an essence: it's because of Sheldon that the group can or can't do something.
It's because of his high intelligence that Sheldon, at times, doesn't know how to act. He takes things too literally, doesn't always understand humor, and is often the butt of the joke. As brilliant and lovable as Sheldon is, he has sad aspects of his life that are upsetting for viewers and his loved ones.
The Death Of His Pop-Pop
It's no secret that Sheldon is close to his Meemaw. Everything she does makes his eyes sparkle. But as much as he loves her, he adored his pop-pop more. In "The Santa Simulation," Sheldon is forced to play a holiday-themed version of Dungeons & Dragons. The game went south when Sheldon's storytelling went off-topic and he started talking about his Pop-Pop. His Pop-Pop was the only person who encouraged Sheldon to pursue science. And when Sheldon was five years old, he asked Santa to bring him back. When Santa couldn't deliver Sheldon's request, he began his grudge against Santa Claus.
Seeing how upset Sheldon was over the loss of his grandfather was gutting.
And The Death Of His Father
The loss of his Pop-Pop wasn't the only death Sheldon experienced at a tender age. Sheldon's dad also died when he was just 14 years old. At this time, Sheldon and his dad weren't particularly close, but it's a loss that Sheldon would never get back.
His father was an alcoholic, an absent parent, and apparently overweight (which is part of the reason he ed away) but it's upsetting that a person as sweet and bright as Sheldon had to endure so much at a prime time in his life. Fans felt sorry for him.
His Secret Storage Closet
Sheldon appears like a very neat and tidy young man. There's not too much clutter in his room or apartment beside his collectibles. But that all changed in "The Solder Excursion Diversion."
When Amy gave Sheldon a new laptop, she told him she would recycle his old one. Sheldon knew he couldn't part with his old laptop, which is when he showed Amy a side of him she'd never seen before. As it turned out, Sheldon had a storage unit filled with everything Sheldon's ever owned. There were toothbrushes, electronics, clothes... Sheldon felt ashamed that he wasn't able to part with his things, which was disheartening for Amy to hear.
His Awkwardness Makes It Hard To Connect To People
Sheldon is a genius, but that doesn't mean he's a genius when it comes to relationships with people. He doesn't enjoy small talk, he doesn't understand humor, and he can be offputting without meaning to.
Over the years, Penny has become a great source of comfort for Sheldon. In one scene, they tried getting to know each other better where they told each other something that makes them sad. Sheldon told Penny that he was upset when YouTube changed their rating system with viewers and it affected him. Annoyed, Penny tries to leave because she didn't think Sheldon was taking it seriously but on the contrary, he was. Sheldon told her she hurt his feelings because people don't take his fears seriously.
His Inability To Understand Sarcasm
Sarcasm is a kind of humor that surrounds Sheldon on a daily basis. Howard is constantly throwing sarcastic remarks Sheldon's way but Sheldon doesn't realize it's a joke. He takes things literally and misses when people are making fun of him. And while he doesn't understand every joke, he does know when he's being made fun of.
To help his situation, Sheldon began asking people if they were being sarcastic or not, and believe it or not that helped him understand it better. He too began playing around with sarcasm and even creating a word for when he was joking: Bazinga!
He Was Bullied As A Child
Sheldon enjoys competition when he knows he's going to win. As soon as he realizes that he's not as smart as he thought, things go downhill for our Shelly. This could stem from his childhood of being bullied. Over the seasons, Sheldon itted he's been beaten up, dunked in a toilet bowl, and had things stolen from him. It's said that those emotions come to a boil when his colleague Barry Kripke comes around. Kripke isn't necessarily kind to Sheldon but he does raise the bar when it comes to physics, which only makes Sheldon work harder. As long as Kripke doesn't poke fun at him, they're cordial.
The Real Reason He Knocks Three Times
Knock, knock, knock, Penny. Every time Sheldon knocks on a person's door, he knocks three times before stating their name. He typically does three rounds of this before he's satisfied with opening the door. Even if someone tells him to come in from the other side, he won't do it until all rounds of knocking are completed.
People judge Sheldon for doing this but it comes from an awkward past time. When Sheldon was a child, he walked in on his father sleeping with another woman. So, not only did Sheldon find out that his dad was cheating on his mom but he saw something completely inappropriate at a young age. To make sure that never happens again, Sheldon always knocks more than once.
Sheldon Can't Relax Outside Of His Routine
The annoying thing about Sheldon is that if he's uncomfortable, the group is uncomfortable. If Sheldon is unhappy, the group soon becomes unhappy because Sheldon becomes intolerable to be around. He demands to be comfortable and feel safe at all times, which can be a burden to guests.
His routine is important to him. He goes to the bathroom at the same time every day, he gets takeout from the same restaurants every week, he watches the same TV show every Saturday morning in his spot... The list goes on. Without his routine, Sheldon is sadly a mess.
One Of His Biggest Findings Was A Blunder
In one episode, Sheldon is "in the zone" with his equations because he believed he found a method for synthetic element. He showed his formula to everyone and was congratulated and adored by all. It was a big day in his career. But after reviewing it once more with Amy, he realized he did it as square meters instead of centimeters. However, regardless of Sheldon's mistake, those at the Hubei Institute for Nuclear Physics still had promising studies because of his math. The entire blunder devastated Sheldon. It made him feel foolish for parading it around while misreading a simple form of measurement.
Unresolved Arguments With Loved Ones
Sheldon isn't good at conflict. He tends to flee, isolate, wallow, and move on from it by digging into his work. Viewers have seen this when Sheldon discussed his former friendship with Tam, his ongoing battle with his brother, and when he and Amy broke up. Sheldon can be selfish and arrogant most of the time but he doesn't know any other way to live or act. He's himself through and through. Knowing that he tried in his own way is all Sheldon can do, and it's upsetting when others don't see it the same way.
