É David Brin - O Efeito Prático .
Da wikipedia:
In this world, instead of objects wearing out as you use them, they improve. This is referred to as the Practice effect. For example, swords get sharper with use, baskets get stronger the more things they carry, mirrors, furniture and decorations look more attractive the more they are looked at. The downside to this being that an object's condition deteriorates over time if not put to use. Under this system, members of society's higher strata employ servants to Practice their own possessions to perfection.
