Self Defense

I took a long walk today in my bare feet. When I got home my feet hurt a little but I noticed that I had developed blisters. As I felt them and thought back to previous blisters it occurred to me that some of the bodies self-defense mechanisms are kinda dumb. I mean what in the world makes the body think that because it is getting damaged by something rubbing against it to separate the outer layers of skin and fill with a clear liquid that will hurt like crazy whenever you touch it? It just doesn't make sense.