I don't know if this has been mentioned or if anyone has noticed, so if it has been then disregard this.
I was out in the field killing stuff and I already had the yellow damage icon. After resting I target another mob, and not being anywhere near it, draw my weapon and I get the Heavy Damage warning. The mob didn't hit me and I hadn't landed a blow on it yet but my equipment still took some damage somehow.
So basically I'm wondering if anyone knows how the wear system works and if you do what are the factors that cause damage to equipment.