in my life time i prob lost close enough to 700-800 fishes after along period of time, due to numerous problems..
e.g. electricity going out during late nite, pump stops workings killing about 3rd of the occupents in my tank (thats happened to me quite a few times actually, and was partly one of the reasons we gave up on our old aquarium about 10years ago)
big, fat, deadly unknown disease hitting the fishes during winter and killing a load of them off.
after a while single fish deaths dont really mean much and no way hurt as much as it does when an entire tankful amount dies off.
but the good thing if u have live barerers is that there population comes back pretty quick.