Many theories hinge on one character in particular.

Often based on an overlooked side character or an overlooked aspect of a main character, these theories imbue a once-minor piece of the fictional world with a whole new significance.

Secret Genius

"Kevin Malone, if not actually a genius, is certainly much smarter than he lets on in The Office. Clearly he's lazy, and gluttonous, and blah-blah-blah..."

"...but after the merger with Stamford, and its revealed that Martin had served time, Kevin realizes that he needs to give plausible deniability to any sort of financial maleficence that the accountants have been doing, and flanderizes himself in front of the camera."

"Occasionally he slips up and reveals himself to be something a math genius, and has to backtrack, and play it off as some kind of Food-based idiot savant."

"It's how he was able to afford ownership of the bar at the end of the series, I'm sure he made a bit just cashing in all those free drinks, but actually enough to buy a bar? I don't believe it."

-- Six_Foot_Dwarf

A Very Suave Red Herring 

"James Bond's primary purpose is to be a distraction to keep attention off the spies who actually spy. Villains and other spies know him, he rarely takes an alias, he makes his presence known early on and keeps messing up operations for the villains..."

"...but other spies have already infiltrated their ranks and work while Bond does as much visible damage as possible to keep the others safe."

-- BettyVonButtpants

More Office Lore

"My own theory that in The Office when Andy proposes to Angela the people playing his parents are different actors because they are literally actors."

"As in he hired them to pose as his 'perfect parents' because his own parents couldn't be bothered to come. The people in the season 9 episode Garden Party are his real parents, who clearly are di**s."

-- cant_Im_at_work

Tough Upbringing

"Ed from Ed Edd n' Eddy is mentally stunted, which is why he's one of the "dumber" characters in the show despite appearing older than the other two Eds (he's about as tall as Kevin and Rolf, who are some of the oldest kids in the cul-de-sac)."

"Also that his parents are abusive to him because of his mental handicap (literally removing the stairs when he was grounded), and his sister's attitude towards him is learned behavior from their parents."

"This is further reinforced by him living in the basement, having non-existent hygiene habits, and 'retreating' into obsession with TV and sci-fi comics.

"In fact, the other two Eds come from troubled homes as well, which is why they're social outcasts in the cul-de-sac. It's been heavily implied that Eddy's parents knew his older brother was physically abusive to him and let it happen."

"Meanwhile, Double D's parents spend zero time with him, and won't even directly communicate with their son, choosing instead to leave him notes for chores instead."

-- Kent_Knifen

Still a Witch 

"Glinda dropped Dorothy's house on the Wicked a Witch of the East, not the tornado, and uses her to gain control of Oz."

"One of the first things Glinda tells Dorothy is that SHE killed the witch. They praise her so she'll accept it, and when the Witch of the West comes along, who killed her sister? Dorothy."

"Glinda then puts the ruby slippers on Dorothy's feet but DOES NOT TELL HER THAT SHE CAN USE THEM TO GO HOME. Instead, she sends Dorothy to Oz in possession of objects that a witch would MURDER her for."

"Dorothy, being forced into a situation where her only salvation is Oz and her worst enemy is the queen inadvertently exposes the Wizard of Oz as a fraud AND murders the Witch of the West."

"Now, who's left to rule Oz? Glinda fu**in' witch of the north. She used Dorothy as an expendable pawn to gain control of Oz without having to leave her bubble. And when Dorothy is done upheaving the two biggest powers in Oz, Glinda sends her home and makes her think it was all a dream"

-- taz20075

Saboteur 

"The Empire Strikes Back: Admiral Ozzel is a rebel spy."

"Everything Ozzel does in his brief bits of screen time is to the detriment of the Empire. When the probe Droid finds the rebel shield generator, Ozzel tries to dismiss it as smugglers before Piet speaks out of turn and gets Vader involved."

"Later, Ozzel orders the fleet out of hyperspace too quickly, giving the rebels plenty of time to activate the aformentioned shield generator that Ozzel knew about."

"'Clumsy as he is stupid' or Rebel sympathizer who gave is life to give the Alliance as much time to evacuate their base as possible? I side on the latter."

-- JustafanIV

What Could She Possibly See in Bowser?

"Peach is totally into being kidnapped, no one who isn't doesn't have that little security" -- Time-Vault

"Even more than that, she's having an affair with Bowser but doesn't know how to leave Mario. Bowser isn't kidnapping her, she leaves with him."

"That's why every time she gets saved she's like 'oh yay, you saved me again.' " -- Good_Cop_Yes_Donut

Other fan theories are based on glimpsed connections between two fictional worlds that hail from different stories.

These ideas propose that two universes once assumed to be disparate are actually linked quite closely, and the linkage can suggest some pretty diabolical transitions.

Classism 

"The Jetsons and the Flintstones are living at the same time in a dystopian future where the 'haves' live above the clouds and the 'have nots' are stuck on a wasted Earth."

"The signs include that Flintstones celebrate things like Christmas and other holidays which doesn't make sense and The Great Gazoo alien appears in both series."

-- lowsodiummonkey

 Beware of Dancing 

"The town from Footloose is the same town from Tremors. The ban on dancing wasn't a puritanical attempt to control the youth."

"The town elders were aware of the graboid threat, and banned dancing out of the fear that it would cause rythmic vibrations waking up the creatures sleeping below the town."

"Kevin Bacon's character in Footloose stayed in the town, growing up to be his character in Tremors, at which point he has to try and contain the danger he inadvertently released."

-- CorporateNonperson

Lots of Talk About Warps

"Event Horizon is a prequel to the Warhammer 40k universe." -- FeasibleBeaver

"The writer, Phil Eisner, tweeted at one point that he plays 40K, so it was definitely an influence on the script. That's as good as canon for me." -- ch1burashka

"YES. It makes the movie so much more fun in my opinion, they probably show this movie to people to illustrate what happens when you go through the warp without a Gellar Shield." -- waywardhero

And last, some people are all about adding a new lens to experience the story through. They jump on a couple key details and fill in a few more.

The result is a brand new--and convincing--context through which we can experience the story we already know and love.

Evidence 

"The reason each It's Always Sunny in Philadelphia episode starts with a date and time is because they're all testifying against each other in court." -- BigDirtii

"If this isn't how the show ends I'll be disappointed" -- Jupigorg

"I really hope they see this" -- AndroidDoctorr

Letting Kids Run the Show

"Pokedex entries are written by young trainers. When a professor sends a bunch of ten year olds out into the world to document Pokemon, of course the "research" can't be expected to be professional in the least."

"This is how we end up with the creepy legends of ghost pokemon that might have been passed around as playground rumors, or impossible facts like macargo being hotter than the actual sun."

"There's no reason why out of all the Pokemon professors, one of them couldn't have revised their dex information and correct the tidbit about pidgeot breaking the speed of light or gardevoir creating black holes or blazikens jumping over 30 story buildings."

"It's likely they leave the kids to their own devices without bothering to fact check, and kids, being kids, are going to exaggerate."

-- cold_french_fry

Layers and Layers 

"The 'real world' in the Matrix movies is just another layer of the Matrix, designed specifically to appeal to people unwilling to conform to the normal Martrix."

"Humans in this outer Matrix have confirmation of their belief that something was wrong, and get to indulge in the fantasy of being a heroic freedom fighter against the faceless evil machines, thus choosing to accept this false reality."

"The anomaly of the One is that he's capable of rejecting both realities, which is the reason why he had powers in the real world."

-- Mikeavelli

Not of Sound Mind

"That Loki was controlled by the tesseract more than he let on."

"His eyes glowed multiple times and he shed a tear when Thor tried to talk sense into him."

-- ELW98

Where He Came From

"In Disney's Ratatouille, the old lady in the beginning of the movie living in the house next to the river is the food critic, Anton Ego's, mother."

"In the flashback scene where he eats the ratatouille you can see similarities of the house from the beginning, her face and I think the bridge."

-- Bev-Low

Just as Scary 

"I 100% believe the two men accompanying the woman in the original 'Blair Witch Project' planned and successfully executed a plan to murder her while they were deep in the woods."

"Too many factors point to good old fashion murder than a supernatural occurrence."

--ThatCoryGuy

Through Dog Eyes

"The monsters in Courage the Cowardly Dog are regular people but seem monstrous from Courage's perspective (since he's cowardly)."

"Also they live in the middle of nowhere because his owners never take him out so that's how he views the world."

-- DaRoosta321