For me, it goes both ways. People who don't know me at all either think I'm incredibly stupid, because I can't hold a conversation, mumble, stutter occasionally, look around when people talk to me, etc.
Some people who don't know me also assume that I'm incredibly smart. For some reason, being quiet seems to make some people think you're incredibly smart, while it makes others think you're an idiot.
As for people who do know me, I think they sometimes expect too much of me.. thinking (assuming) I can handle something I can't & not understanding that I'm unable to do certain things.
Also, some people who know me think I'm an idiot, for the very same reasons people who don't know me... my inability to speak coherently at most times, in most situations.
I, personally, consider myself to be a very smart person, who has the capacity to be much smarter, if I only had some help with understanding & doing certain things.
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?Be who you are and say what you feel because those who mind don't matter and those who matter don't mind.? _Theodor Seuss Geisel (Dr. Seuss)