Using “I” and “me” has always created confusion among learners of English (here I might include myself as well). For some reasons I have never though seriously about this (until a couple of years ago) although I knew there are mistakes in my usage of these pronouns.
According to my experience as a teacher the vast majority of learners of English (at least the Vietnamese learners of English) use “me” instead “I” and not vice-versa. The mistake particularly occurs when more than a subject is used in a sentence.
My friend and me went to China last year. (Wrong)
My friend and I went to China last year. (Correct)
The first person personal pronoun can take two forms:
Subject of a verb – I
Object of a verb – Me
As a subject of a verb, “I” is usually (if not always) placed before the verb and refers to the person who does the action of the verb. Basically, it is the subject of the sentence.
I live in Vietnam.
I bought a new house.
As an object of a verb, “me” is usually (if not always) placed after the verb and refers to the person affected by the action of the verb.
My wife told me to cook.
She left me alone.
I can give you uncountable examples when native speakers of English make this mistake. Why is this happen? Probably ignorance will be the proper answer.