What is the deal with self sabotage?

Why would anyone "sabotage" their own success? It doesn't make sense that we would ever do such a strange thing. Yet we do it all the time.

Not only do we do it all the time, most of the time we don't even know we are doing it. We can struggle for years trying to breakthrough in a particular area of life and not even notice that we are making the same mistakes over and over. People around us can see it but we don't always notice it ourselves.