I can't help wondering if you beat the crap out of the dude who used your knife to attempt removal of staples capable of breaking an inch of the tip off your Endura.
I don't imagine that many people here would be very sympathetic if you yourself had done it -- but if it was a friend who did it, I guess it's just a lesson in
never ever letting anyone borrow a knife from you if you care about it, because this is what they do. Foolish things. Things people do when they are using someone
else's tool and figure they don't have to care about it.
A genuine staple remover can probably be had from any of numerous "dollar stores," and save your knives from disaster. Even if the tip hadn't broken off, the edge probably would have suffered some regardless, so it's worth investing in the right tool for the job.
Sorry about the damage to your knife. You should probably hit your friend up for the cost of replacing it. A good friend would have done so without having to be asked, in my view. But I would not stand on ceremony: if he didn't offer on his own, I'd politely demand it -- unless I had told him, "Sure, go ahead, remove those staples with this knife of mine."
-Jeffrey