Part of it is that being cut by a piece of paper is a bit humiliating. However many times it happens it feels like soem kind of insult.

That's probably related, at mental level, to the physcal thing that JohninKansas emotions - the body feels it's so insignificant it doesn't help out with pain reief. So we have a double insult to deal with. The paper is saying "thought you were so touch - can't even beat a little piece of paper", and the body is saying "What a wimp you are..."