You make a good point - I need to distinguish between two different things: one is if you are genuinely trying to hide the fact that you're upset because you really don't want anyone to know (which could be for many reasons), such that when someone asks what's wrong you lie and say "nothing" because you genuinely are trying to hide it. That may be because you just don't want to talk about it, and that's fine. But the other type is what I was referring to above, which is when you are trying to actively display that you are upset, you want the other person to know that you are upset or seem upset, yet when they ask what's wrong you then deny that you are upset. That's a manipulation tactic because you are intentionally putting out those vibes in order to string someone along and make them ask after you, but then denying them an answer, it puts you in a position of power and control over the other person and "forces" them to keep asking after you. That's why it's a controlling behaviour. Hope that helps :)