People screw up. And in movies, you'd expect that when someone screws up that those scenes would just be played for laughs as outtakes or on a blooper reel. But sometimes everything else about the scene is so good and the screw up is so unexpectedly perfect for the movie that the directors include the screw up in the final film.
Screen Rant provides 10 fun movie mistakes that should have been outtakes but ended up in the official version of the film below. The lesson: always keep the camera rolling.