Fundamental Attribution Error
This is a classic example of human psychology at work. In the literature what you are describing is very similar to what psychologist call the Fundamental Attribution Error. It is our way of describing the behavior of our selves and others. We tend to blame external factors on our decisions so we relegate blame to something out of our control. Where as we tend to blame internal factors on others behavior as something in their control.
I believe the reason we do this is because our mistakes have a direct impact on our self-worth or self-esteem. Whereas other people's mistakes don't impact how we view ourselves. Its is definitely an ego thing. To admit a mistake one has done, hurts the self and our view of who we are, and as with every other animal we tend to avoid pain. The psychological pain of admitting a mistake is too great for us so we avoid that pain by blaming external factors. Studies show depressed individuals see "reality" more clear, they are more honest in explaining their past mistakes. Evolutionarily, depressed individuals are less productive and helpful so these defense mechanism evolved to prevent that state of mind I believe. The problem is that we are so convincing in our rationalization it is hard for us to see how we created the problem in the first place and that is where psychology comes in, the biggest question in the field, how do we get people to understand themselves and change for the better?