Firstly, having read your posts, you don't come across as stupid to me.
Secondly, the sort of things you are describing sound very familiar: I always don't realise things that I somehow should have realised. I get called dumb for it.
I think that most people work within a certain set of assumptions, and they assume that anyone who looks normal will also work within these parameters and thus know all these "really obvious" things. We may look normal, but we are not neurologically typical, and thus we do not automatically know all these things that we know, and we will not necessarily make the same inferences, given the same information, that a neurologically typical person would.
Not stupidity, just difference.
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Music Theory 101: Cadences.
Authentic cadence: V-I
Plagal cadence: IV-I
Deceptive cadence: V- ANYTHING BUT I ! !! !
Beethoven cadence: V-I-V-I-V-V-V-I-I-I-I-I-I-I-I-I-I-I
-I-I-I-I-I-I-I-I! I! I! I I I