Imagine standing in the corner of a room. With both eyes open you hold a pencil

Imagine standing in the corner of a room. With both eyes open you hold a pencil at arm's length in front of you, placing the pencil in the corner. Now close your left eye and observe what happens tot he image of the pencil. Alternate by closing only tour right eye and observe what happens.

This illustrates that humans have a dominant eye just as they write with their dominant hand and descend stairs leading with their dominant leg. If the pencil remains in the corner with one eye open, this signifies the dominant eye.

If the pencil moves to the side, this means it is not your dominant eye. Which is your dominant eye? Explain why you know this?

So my dominant eye is my left eye but I don't know why that is or anything. Any help would be appreciated. Thanks in advance