“I” is Not a Noun
I learned what you learned; a noun is the name of a person, place, or thing.
And you and I are none of those.
Yet I must still use “I,” and it is structured in our language to be the subject in a sentence: the doer of the action, which is a verb, doing it to an object, another noun. But the self that we call “I” is not really a noun. Language has its limits.