Mono, like most other types of fishing line, will eventually wear out and lose its strength and stretching ability. If your fishing rod and reel is exposed to sunlight, the UV rays will cause the quality of the mono line to break down, which weakens it and can lead to broken lines, lost lures, and fish getting away. It’s a good idea to swap out your monofilament line every year in order to avoid any issues with the quality of the line itself.