No matter how powerful a weapon or armor becomes, it still suffers general wear and tear. Weapons and equipment degrade the most when you are defeated in combat. To check your equipment’s durability, hover over the item. The item's durability is represented by a numerical value, and if it reaches zero, the item is ineffective until repaired.
When an item is nearly broken, a yellow indicator appears on the near your portrait. When that icon turns red, the item is completely broken is no longer useful to you. Hover over this indicator to see which items in the inventory are in urgent need of repair. Regularly repair your items through any vendor.