After level 10 your items will all start to lose durability when they are used. This loss is very slow, but if you die in normal more (not Hardcore) your items lose 10% durability. They still function, but you need to repair them before they get to 100% or they won't be usable until they have been repaired.
This trophy pops the first time you use a vendor to repair your items. Nearly all vendors will have a repair tab that can be used to do this.