I have the perfect answer, in case of overwhelming friends that ask „what things?”, when you say „I can’t, I have things to do” at their try to absorb you into some personal plan.
It’s „why are you interested?”. I bet the upcoming line is „just curious…”, when the truth is more like „I just want to mock your reasons, and convince you to abandon them, in order to do what I want, because a true friend doesn’t refuse what is asked of him”.
It’s a common unintended egoism, and if it’s not understood and opposed (kind, but firmly), it generates a lot of repressed unsatisfaction within the relationship.
And it’s a lose-lose situation.