This poem tells us that people are all the same "nobody" because they conform and become the same person without knowingly doing it. Although these people are different inside they actually seem to appear the same in groups and jobs. There are tons of people that think they are "somebody's" because of their fancy jobs and cars, but Emily Dickinson tells us that they are exactly the same as the person they are sitting next to on the bus when their car breaks down. "Don't tell! they'd advertise - you know!" here Dickinson tells us that we shouldn't tell people we are a "nobody" because that would really make them think of you as an inadequate person, but the truth is if you know you are a "nobody" you will be better off (4).
It also seems that she is talking about celebrities because she says "How dreary - to be - somebody! How public - like a Frog-" which makes me think of famous people because they don't have any privacy because their lives are "public", but we still want to be like them (5-6). In this poem Emily Dickinson helps us learn that we should stop thinking highly of ourselves because we really are just like everybody else.
Charters. Literature and It's Writers 3rd Edition. Boston, MA. : Bedford/St. Martin's, 2004. p. 870