What is the speaker of the poem proud of being I’m nobody?

I'm Nobody is a short, playful poem by Emily Dickinson. In this poem the speaker  claims  to be "nobody" and seems very proud of it. Obviously a person cannot literally be "nobody" because everybody, by definition, is somebody. In this poem  the speaker  is  proud to declare she is not a self-promoter, someone who blows his or her own horn.