because a person is a person
The first person is I or we; the second person is thou or you; the third person is he, she, it or they. There is no fourth person.
These are different points of view in literature. First Person is told from the character's perspective and is distinguishable by the use of words like "I", "me", and "myself". Second Person is...
First person is the one speaking. Second person is the one being speaking to. Third person is the one who is being spoken of.