I think we confuse fault and responsibility too much, as though if we can fix fault on someone else that will absolve us of responsibility. "It's your fault this happened, so it's not my responsibility." Hah! Would that it were all so easy, eh?
Questions about fault are usually covert attempts to escape responsibility, especially if they focus on blame. Figuring out who did what can be part of understanding our own responsibility, but that doesn't define it.
Responsibility is about I did. If I'm involved in a messy situation, then unless someone held a gun to my head, I'm responsible for my own bad behavior.
I really hate situations where I'm handed a lot of fuel for focusing on the other person's faults instead of my own responsibility. If someone else has obviously messed up really bad, I'm happy to focus on their faults and lack of responsibility. Yet, that doesn't really get me anywhere, does it? Once in a great while, you can actually convince a person that they need to take more responsibility for a situation, but mostly they do this on their own or they don't do it at all. So, I'm better off focusing on what I did or can do.