What is this invisibilty about?

From the moment I opened Invisible Man and began reading I couldn’t put it down. The plot advances quickly and automatically hooks the reader. As I read about the journey of the boy and Mr. Norton, I was on the edge of my seat. I was so interested in what was going to happen- was Mr. Norton going to be okay? Was the boy going to be expelled from the college?
I also found myself asking questions about the theme of invisibility. I am already wondering why the author chooses to make the main character “invisible.” The novel opens with the boy talking of his invisibility. He is invisible he says because “people refuse to see me.” Has there been some event in his life that has made him feel invisible? Invisibility for the boy is also aided because the author chooses to keep the character’s name anonymous. Though the reader can identify with the boy, not knowing his name makes him somewhat invisible to the audience. The effectiveness of being invisible has not yet become apparent to me, but I know it is very significant to the main character’s story and to the novel as a whole. I don’t know yet if it is a depressing invisibility or something that is happily accepted by the boy.