What details explain what causes the narrator to begin to "bump people back"? How do these details contribute to the text's overall message?

Hello. You forgot to warn that this question is about the "Invisible Man" prologue.

The text shows details that prove that the narrator exists without being perceived by anyone around him, so he starts to push people to prove that he exists. These details help to convey the message that not being noticed is lonely and that it makes a person doubt his own ability and relevance in the world.

Explanation:

The narrator is an invisible man. This causes everyone in the world to ignore you. His existence is irrelevant to the universe and all people follow their lives as if he does not exist and he is not noticed by anyone, this makes everyone bump into him all the time.

This makes the speaker live an extremely lonely life and makes him start to doubt his own existence and to prove that he really exists he starts to push people back.

The main message of the text is to show how human beings need attention, to validate them, to show that they are relevant. When that attention is withdrawn, human beings can respond with hostility as a way to resolve their internal doubts.