I Think Therefore I Am Stupid

I’m a PhD student with a 4.0 (first term) and 3.75 (second term) GPA.
I earn a considerably decent income.
I can spell the word concupiscence
And even use it in a sentence.

I’ve read some books, which I understood (I think)

But mostly, I think I’m stupid. (I can’t help it)

But frankly, so is everyone.