Durability comes first. But function is also important.
When we make a Briefcase, we make a Briefcase that will last. Also from a functional point of view. That’s why we don’t add a lot of special compartments that are designed to fit items that are popular today (e.g. an iPhone). And that’s is why the Briefcases we made 20 years ago were not designed to fit items that were popular by then (e.g. the movable telephone including a 10 kg power aggregate).
Durability can be a restriction on function. One thing we don’t use is zippers. It’s not that we don’t like zippers as such. On the contrary, we consider it to be an amazing invention. We prefer buttons to our own jeans, but we respect people who have zippered flies. The reason we don’t use zippers, is that they don’t last as long as we would like them to. In stead we have numerous constructions based on flaps that are sealed either with mechanical locks or with a hoop. The hoop construction is our favourite one, since the hoop can be made either my metal or by gashing the leather.