Continuity is a hard mistress. It’s about small details. But if you miss something it can really ruin a movie. The reason for that is that instead of focusing on the story, the viewer is suddenly busy trying to figure out the things that don’t make sense.
Take this (alleged) story from the production of Skyfall. This story has surfaced now, coming as a double tweet (due to twitter video limits) from journalist and filmmaker Charlie Lyne. Now, Skyfall is 4 years old, (and I am not sure if this story is true) but even if not it has a great lesson: