We all do it but most certainly not on purpose—except for major jerks. When situations arise and we can't get things right, it is natural to look for a reason and solve the problem by leaving it where blame lies. However, the way our minds work doesn't always give us the truth. Our self-preservation kicks in, and we are looking everywhere except at ourselves.
Children do an excellent job of shifting blame. They don't want to see how their lack of self-discipline is why things aren't working out for them. They make the problem all about how the parent(s) hasn't gone along with their last-minute demands. This same generalization can be applied to the student-teacher relationship. It just has assignments and participation on the table. And no, I am not freshly traumatized or anything. I do not know what would make you think that.
Adults do this blame seeking too. Like children, we immaturely fall into the old game of looking everywhere except at ourselves to find who/what could have done/gone differently. It's almost like a disease of the heart if we don't stop though. It can get so out of control that we end up flat out lying to ourselves, and that is a great disservice to everyone around us. A great deal of pain and bad relationships ensue. We have to take responsibility for how we affect others, or we won't ever have better outcomes.
Even still, there is a flip side to this train of thought. Sometimes we take on too much blame. Sometimes we take on blame that is not ours whatsoever. That is shifting blame as well. And none of it is good for us.
I am guilty of both types. I do count one of my finer qualities as working very hard at rooting this out of me though. As soon as I find myself in error, I do all I can to make things right—even if it means I have to swallow my pride and apologize to people who are unforgiving. I just do it anyway. It's on the other person if they don't want to forgive after I've done what I can to make it right.
Shifting blame is a natural response, but it is possible to rise above it. In truth, it is imperative that we do if we are to reach our potential to love ourselves and others more fully.