The Big Bang Theory's Steve Molaro Now Regrets Adding Sheldon's Knocking Habit

It's no secret that Sheldon Cooper (Jim Parsons) has some quirky habits that stick with him throughout all 12 seasons of "The Big Bang Theory." There's his fierce preference to always sit in the same spot on the couch, his deep passion for all things trains, his "Bazinga" catchphrase, and his "Soft Kitty" musical tradition whenever he's sick.

However, there's another habit that's synonymous with Sheldon — his knocking pattern before opening any door. Whether he needs to speak to Leonard Hofstadter (Johnny Galecki) in his roommate's bedroom or neighbor Penny (Kaley Cuoco) in her apartment across the hall, the pattern never fails. He knocks three times, says the person's name, and continues this another two times.

Over the course of "The Big Bang Theory," creators switch up Sheldon's knocking tradition. There are angry variations and even a meek one when he goes to Penny's place to apologize to her. Sheldon's friends — especially Penny — can't help but try the knock from time to time. At one point, Penny gives it a chance and actually enjoys the repetitive process. Sheldon tells her, "I bet that started off as a joke, but by the third one, you realized there was something strangely enjoyable about it." She answers, "I kinda wanna do it again."

While it's hard to imagine "The Big Bang Theory" and the character of Sheldon without this knocking habit, there's a dark reason behind why he can't enter a room before completing this ritual. In fact, producer Steve Molaro regrets even putting this particular quirk in the show.

Sheldon's knocking habit isn't something he always did. On "The Big Bang Theory," he reveals to Penny the traumatic manner in which it began. At 13, the child prodigy returned home early from college spring break because they ran out of math to teach him.

"My mother was in Bible study. I walked in the house expecting to find it empty and I heard a sound coming from my parents' bedroom," he tells Penny. "When I opened the door, I saw my father having relations with another woman."

This is why he never opens a door without knocking three times. Though this explanation certainly provides much depth to Sheldon, "The Big Bang Theory" creators didn't anticipate the unfortunate impact this would have on the child version of Sheldon (Iain Armitage) in the prequel series "Young Sheldon." Since the extramarital activities of George Cooper (Lance Barber) are part of the canon, they must be included. Though George hasn't cheated on Mary (Zoe Perry) just yet, he's getting a little too cozy with Brenda Sparks (Melissa Peterman).

In the book "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series," producer Steve Molaro said, "[W]e were just trying to find a way to add some weight and importance to the scene when he said it [to Penny] and that was a way to do it. Had I known it would end up having an impact on Young Sheldon, I might have thought twice about it."

Still, some fans are optimistic that Sheldon didn't witness what he thinks he did, and that "Young Sheldon" can take this plotline in another direction. On Reddit, u/SweaterWeather4Ever said, "On TBBT Sheldon tells Penny he saw his father 'having relations with another woman.' The discreet euphemism is in keeping with Sheldon's character but it is also vague enough to give the YS writers a lot of leeway as to what to depict."