What is the best way to avoid responsibility for your own fault – whether it be work, school or relationships? That’s right, put all the blame on the other person, and it doesn’t matter that this other one is completely not to blame for your own incompetence. The more furiously you insist and the more offended you look, the more effective this strategy will be in the eyes of other people.
First, the OP sent out emails to all colleagues that they would be unavailable for a whole week. Then they prepared special instructions for subordinates who were to take over the work with certain clients in their absence. Moreover, the OP specifically shared all the necessary information with each colleague, so they went to the resort in full confidence that everything would go perfectly.
The subordinate’s reasoning was, as they say, ironclad – as technically that lost client was the OP’s, and the blame, in their opinion, lies largely with the supervisor. Moreover, as the OP admits, nobody around even cared that the manager did not bother to collect the necessary files in advance.