Before everything ever produced could be uploaded to the eternal collective memory bank that is the Internet, film footage was stored on reels of extremely flammable material that tended to ignite like scrolls of black magic with alarming regularity.
Consequently, thousands of classics have been lost to your average human foul-ups and jackassery. But recently, copies of a handful of famous old movies once thought lost or destroyed have been found, with results ranging from "neat" to "unfortunate."
4 Lost Footage from Return of the Jedi
Never-before-seen footage from Return of the Jedi resurfaced on an old LaserDisc after lying undiscovered for 30 years. For those of you too young to remember, LaserDiscs were essentially the predecessor to DVDs, only they were roughly the size of a truck tire for no apparent reason. Lucasfilm used to store and edit all of their footage on them, which probably means there are stacks of undiscovered Howard the Duck LaserDiscs lying in a cursed warehouse somewhere.
"Boy, this technology will never fail!" -Lucasfilm