If everything goes according to plan, I'll spend a few weeks in Canada this september. One of the things I want to do is see bears catching salmon. Of course, using my 50mm prime lens would lead to either extremely small bears on the photos, or extremely dangerous situations for me, so I'll need a telelens.
Decent telelenses prove to be quite expensive... Sure, a Canon 800mm would be nice, but if I spend €13.000 on a lens, Canada will have to wait a few years. So... Compromise and get something that might not be completely what I want, or see if I can get something second-hand.