For example, assuming a passage in a story where a protagonist enters person X's house and a particular room is described in much detail. The described detail does not necessarily advance the story but instead does "character building" hinting at the personality of person X. There literally could be a loaded gun hanging on the wall because X is a secluded hunter living in a cabin. Is this then a violation of the principle?
Edit: I've recognized the principle a few times, mostly in TV shows with lingering camera shots on seemingly unrelated objects, and as another commenter mentioned, it can frequently spoil a surprise twist. There is also a vague line between spoiling the twist and foreshadowing.