The problem I have with "show don't tell" is that sometimes you have a somewhat irrelevant fact, which is not important to the whole story or character developm

The problem I have with "show don't tell" is that sometimes you have a somewhat irrelevant fact, which is not important to the whole story or character development, but you need to state it to explain why the character took some course of action in a particular situation. If you decide to "show" instead of "tell", you would waste your readers time to "show" something not very relevant, which could be simply "told" and you could get on with the story.