There was a story a few years ago about how the awful AI in Aliens: Colonial Marines was improved by fixing a single spelling mistake buried within the game's code.
Aside from raising the question of "why the hell do people care about Aliens: Colonial Marines this much?" this story was a perfect illustration of how insanely difficult video game development is.
Fixing errors, squashing bugs, and generally just ironing out the kinks can feel like finding a needle in a haystack, and even with hundreds of people working on these things, small mistakes can still slip through the cracks.
One way this can happen is when certain bits of content - whether it's a gameplay feature, a random cutscene, or a spoilery easter egg - are accidentally left in the finished product, with the devs forgetting to remove this content on the hectic road to shipping their game.
There have been some funny, highly bizarre examples of this over the years, from relatively minor content slips that can be laughed off by the fans, to monumental screw-ups that will probably keep the devs awake at night for years to come...
8. The Alternate Ending (Shadow Of The Tomb Raider)
Unless you're talking about Infamous, or Quantic Dream's recent games (or some other title with a heavy emphasis on player choice) video games usually have a single, definitive ending. And even in those rare cases where multiple conclusions can be unlocked, only one of them is usually considered canon, like the heroic ending in Infamous 2.
2018's Shadow Of The Tomb Raider did things differently here though, with Eidos Montreal considering multiple post-credits scenes during development. And not only that, but they even went ahead and built some of these alternate endings, fully aware that only one of them would make it into the final product.
Or so they thought.
As discovered by a fan who played an unpatched version of the game at launch, the devs had forgotten to remove one of these alternate sequences, which showed Lara Croft receiving a letter from Jacqueline Natla, the villain in the original 1996 Tomb Raider game.
The ending that players were supposed to get was totally different, showing Lara sat at her desk while pondering the uncertainty of her future.
What's funny about this situation is that some players got the proper ending, while others got the non-canon one. So there was quite a bit of confusion on message boards when people started discussing how the game wrapped up!