Solid logic there, RogerP. I feel like I've learned to appreciate shell over time, having a few pairs, seeing many more on SF. If it was less durable than calf (assume shell was highly prized yet very delicate) then I definitely wouldn't even consider shell. So it's durability is definitely "a" (but not the only) factor in choosing shell over calf. At the same time, it seems that sometimes people understate the durability of calf when promoting shell as a "lifetime" shoe. There are a lot of examples of calf shoes lasting 20-30-40 years, and there are many NOS//deadstock calf shoes from the 1920s/30s/40s/50s available for purchase that are still supple and "as good as new." Shell is more durable than calf, but it's not like all calf dries up and shrivels away after 5 or 10 years. Some people just don't like how calf creases - all the little hairline cracks - but that's a different issue (same as if you don't like how shell looks).