If you're a true 90s kid or had at least a halfway decent childhood, then you've probably watched "Hey Arnold!" While it was probably one of the best classic Nickelodeon shows, there's a dark theory behind it.
Arnold's grandparents really weren't his "grandparents." They're actually his real parents and the story about his parents getting lost after a plane accident is a just a lie. Gertie and Phil, the grandparents, had Arnold at a rather elderly age and unfortunately for Arnold, this led to some health conditions.
Arnold was born with hydrocephalus, which gives Arnold his uniquely-shaped head. Arnold's name was actually inspired by a specific form of hydrocephalus, known as Arnold Chiari Syndrome. But wait, Arnold isn't the only one with an oddly-shaped head! Yes, this is where another one of Arnold's health conditions comes into play.
In the real world, Arnold is severely bullied for the shape/size of his head. All this distress paired along with his conditions allows him to hallucinate a world where everyone has oddly shaped heads. This helps Arnold feel normal, because no one can make fun of his head because theirs are equally f*cked up.
So where did this idea originate from? Some claim that the creator of the show had an encounter with the child of two rather elderly adults. The child was noticeably mentally unstable and spoke of his imaginary friends and their wild adventures. It's said that the creator had gained permission to share the boy's story and in exchange he would improve his life. Instead, the creator broke his promise and got rich by making a TV show (douchebag).
So is any of this true? Nope. Craig Barlett, the creator, actually got the inspiration for the show based on who he was as a kid, a vivid daydreamer. Bartlett had always wanted to make an animated series. While working on "Rugrats," he approached Nickelodeon and told them about his vision.
So where did the dark theory come from? Fans of the show always wondered what had happened to Arnold's parents. Bartlett really hadn't thought of a solid backstory for his parents yet, so fans started to make their own. This resulted in fans believing that the parents Arnold always envisioned did not actually exist, and that his grandparents are his true parents. This theory spread rather fast, faster than Bartlett could release an episode explaining the parent's backstory, and so the theory lived.
Luckily, Arnold is not the result of delusional elders. Arnold is just a regular boy who lives with his crazy grandparents in a neighborhood of oddly shaped people. Moral of the story: explain everything to your fans or else they'll ruin the reputation of your show and you.