Why would a garage spring break?

A garage spring would break due to metal fatigue, wear, and environmental factors that weaken spring over time, as springs store high tension and cycle thousands of times lifting heavy door. The most common reason is normal wear and age, as torsion springs are rated for about 10,000 cycles, meaning one open and close is one cycle, so with average use of 2 to 4 cycles per day, spring lasts 7 to 10 years before metal fatigue causes coils to crack and snap with loud bang. Lack of maintenance like not lubricating spring with silicone lubricant twice yearly causes friction and rust that accelerates wear and corrosion, weakening steel. Rust from moisture, especially if gutters above garage overflow onto door and springs causing water exposure, causes pitting and weak spots that break under tension. Improper spring size or low quality spring installed that is undersized for door weight causes overstressing and early breakage. Cold temperatures make steel more brittle and can cause breakage. Door that is unbalanced or off track puts extra strain on spring. Cheap springs with lower cycle rating break sooner. When one spring breaks, other spring is also near end of life due to same age and cycles. To prevent breakage, lubricate springs, keep gutters clean to prevent water damage, and consider high cycle springs rated for 20,000 cycles that last longer.