From what I have witnessed over the years, people are embarrassed of being caught and go on the defensive instead of calmly thinking about it and reacting after things cool down.

I'm not saying that everyone is, by any means, but the majority of my experience with it is embarrassment.

Now the sad thing is that they usually aren't embarrassed about their actions but the fact that they got caught. I think it's hard to take when you think you are smarter than everyone and then you see that most people saw you coming a mile away.