It always boils down to definitions probably and sometimes defining terms itself is just so difficult. So, let me take help of some examples.

Let us say I borrow a book from you. I am choosing a book as it’s relatively petty, but you could replace it with something more valuable or dear — a camera, jewellery, pet, kid etc. Now, I would feel it’s my duty to keep that book safe and in good shape till I return that to you. I call it my responsibility. If I spill a cup of coffee on that book, I am going to be upset with myself. Is that being too serious? You could say that I am upset because I think you would be unhappy with me returning you a soiled book, but even if I knew you were not going to care much, I would feel guilty myself.

On the other hand if someone else had taken the book from you and spilled coffee over it, and returned it to you without any remorse, I would still not be able to empathise with the person. I would probably feel like — how could someone be without any sense of responsibility.

In the greater scheme of things, like you said, no one is responsible for anything. But then we are not going to condone drunken driving or medical negligence. I am also not saying that my feelings in the above case (of spilling coffee over your book) is justified or is how it should be. I would like to know how you see the case though, and how you resolve the apparent paradox between what I call taking-things-seriously versus being responsible. This sense of responsibility is not towards me but towards any other person involved. I could be irresponsible towards myself, but if we start being so towards others, and if everyone was to be so, how would we as a society function?