Any time work of any kind is done some energy is lost. In every mechanical operation a certain amount of energy becomes unusable, spread out into random, disordered molecular activity in the form of sound waves or increased heat. If you apply directed energy to boards and nails using hammer and saw in order to build a doghouse, some of the energy has the desired effect, but much energy is dissipated in the sound of the hammer and saw, heat in the boards, nails, and surrounding air, etc. This fundamental law of physics is also often stated as the law of increasing entropy . Entropy refers to the amount of energy that cannot be converted into mechanical work.
High entropy refers to a state of great disorder.
The effect of this law is that unless there is a purposeful source of energy operating in a system, the various parts, molecules, etc. become less and less organized and more and more random. Men can build houses, automobiles, watches, computers, etc. by application of purposeful, directed energy. Some of the energy used to effect this decrease in entropy is lost in the process in the form of sound and heat energy. A certain amount of the useful, directed energy used to construct these organized things becomes useless. A house will eventually become a mere pile of rubble unless additional directed energy is used for upkeep.