It's just a minor thing.
Is it the people that don't know you, except on a very impersonal level, that can tell when you are least happy? Even when you don't realize it? Is it that the people close to you don't notice the slow transition from elated to ---- ? Or are we just easily mislead into believing we are unhappy when people we rarely talk to say something about our state of mind twice in one day? Why is it so easy for everyone else to know when they are happy, sad, mad, etc. but not for me? Why do people who express an interest in me terrify me?