I do alot more casting when I fly fish, which might be a result of my poor casting skills. But even if I am not false casting to dry my fly, I will need one or two at least to shoot retrieved line, when stripping streamers, or upstream nymphing. Also I don't do much wading when tossing lures or bait, and wading a fast moving stream, and holding in the current is definitely more fatiguing. I get quite tired when fly fishing, but IMO it is a good tired. So the idea that if one is getting tired one should quit, does not make sense to me. Alot of things I enjoy doing are tiring, and tax my body. This is a good thing.