Heat is the enemy of electronics and mechanical systems. As current flows through a wire or a processor, heat is generated ($I^2R$ losses). If a component runs too close to its maximum rating, the internal temperature rises, degrading materials, melting insulation, and causing premature failure. Derating keeps the temperature down.
Manufacturers provide "Derating Curves" in their datasheets. These graphs show a straight line sloping downward. As the temperature rises, the allowable power dissipation drops. derating factor
Several factors influence the derating factor, including: Heat is the enemy of electronics and mechanical systems