What causes durability loss?

[adeyke]

For the weapon, hitting things.

For the armour, getting hit.

Er, that sounds overly simple, but it really isn't a complex issue. When you successfully hit things, there's a chance the weapon gets damaged. When you get hit, it picks an armour slot and there's a chance that the item in that slot gets damaged.

EDIT: Of course, there'd also be the exceptions for which skills lower durability and which don't. For example, blade fury doesn't affect weapon durability while blade shield does.