"Cause", I believe, is misused here based on what the article describes. It "causes" tension in the same way poorly written code produces bugs "caused" by improperly handling an input that should have been expected and coded for.<p>Edit: To clarify- figuring out decorating styles, putting items together after purchase... these are not "unanticipated inputs" in a relationship. If they're throwing errors, the only reason Ikea is involved here is because they instantiate the $homeFurnitureStore variable more often than other possible places.