#"Conservation of mass!"# is a fundamental, underlying principle of chemistry. In every chemical reaction that has ever been performed, mass is conserved. What does this mean? It means that if you start with 10 g of reactant from all sources, AT MOST you can get 10 g of product. And in practice, you are not even going to get that.
This illustrates the principle of stoichiometry:#"garbage in equals garbage out".#