Energy runs down or wears out and is depleted from the system.
This law about thermodynamics, the entropy of a closed system, can never be halted nor decreased. It's strongest change, or inclination, is to tend to deplete at an increased level of measure. Or, simply stated, the amount of energy needed for a specific work will be greater than the work so that entropy results in lost energy. The greater the work need will result in greater the energy lost. Thermodynamis is a physical theory of great generality impinging on practically every phase of human experience.