Why can't people just be themselves?

i could never understand why people assume you are sad when you are not, I mean I internalize negative things but I am very very confident. People get to me a lot but its always things they do .... if we get deep I guess you can say that comes from programming but thats another iffy kind of insecure...not the I wonder what he thinks of me type. It beats me, why people assume you are being emotional when you share for example an insightful quote about life or express any kind of emotion. Why can't people just value the human spirit....why are people just afraid of expressing themselves...