Which law implies that energy transfer is never 100% efficient?

The Second Law of Thermodynamics states that in any energy transfer or transformation, the total entropy of a closed system can never decrease over time. This principle implies that energy cannot be completely converted from one form to another without some energy being dispersed as waste heat, resulting in inefficiency. This inherent increase of entropy means that, while energy is conserved overall (as highlighted in the First Law of Thermodynamics), the usable energy available for doing work is always less than the total energy input into a system. Thus, this law emphasizes that no energy transfer can be perfectly efficient, as some portion of energy is inevitably lost or transformed into less useful forms during processes.