Why do I keep thinking I'm stupid?

if I know im smart why do I think im stupit...

because just for the fact you think you KNOW something (know as in the undisputed truth for you) hows why people may call you stupid...

but I dont know you so I cant judge

I must say, you think you are stupid because your sefl-esteem is low. And that comes from people(family members) calling you or naming you stupid. You need to stand-up for yourself. It's so great that you know that you are smart. I would like to tell you to STAND-UP for yourself. Don't let others pull you down or discourage you by telling you or saying to you that you are stupid. CLAIM it that you are not stupid, say I am SMART!

How can you simultaneously know you are smart and think you are stupid? That doesn't make any sense.

you think you are stupid possibly because you spelled stupid wrong in the first place...