Nibs wear with use just like traditional media - pencil, charcoal, and pastel or any tool. Maintain pen performance and protect your Wacom device by replacing the pen nib before it is worn to a sharp point or gets too short. Not replacing worn nibs can damage the your Wacom device.
For which nibs to wear with your device, please consult the product manual: Where do I find the manual for a Wacom Device?