There are 3 common reasons for a weak trimmer line: 1) Impact from solid surfaces: Depending on the design and materials, each product has its durability level against hard surfaces. Most home-use trimmer lines break easily upon contact with the pavement or rocks. 2) Mismatching the trimmer’s size: Even the best line trimmer has the breakage issue when it has the wrong lines. Manufacturers have exclusive lines that can only be compatible with their products.  When buying replacements, gardeners need to check if the brand has the parts for purchase. Otherwise, choose the product with the correct size for the tools. 3) Corrosion from the climate: Dry seasons like the winter decrease the line quality at a fast pace. Frequently removing debris and grass helps maintain durability.