Okay, I guess, for some, spoilers ahead. Again.
But you may know this already. After a number of adventures with his friend Dr. John Watson fought directly with his most formidable foe, Professor Moriarty. Both went over the Reichenbach Falls. This battle, depicted in "The Final Problem", meant the end of Sherlock Holmes.
Except! Years later, Holmes reentered Watson's life, alive and well, with an explanation of how he'd survived and what he'd been doing in the time since. See "The Empty House." It may have been the first retcon. While there were mythical figures with contradictory stories, it was almost unheard of for a single author to publicly change his depiction of what had happened.*
Arthur Conan Doyle hoped for an august literary career and he intended for Sherlock Holmes to be but a small part of it. That's why he attempted to kill his own creation to begin with. Obviously, he couldn't quite pull it off. Holmes was just too big. Although some speculate that he kept some ambiguity from the outset so that he'd still have his options open. It's a plausible idea.
*At the start of Adventures of Huckleberry Finn, Huck says that Twain "stretched some things" in Tom Sawyer, but as far as I can recall nothing in the later book specifically contradicts anything in the earlier one.