yield and purity in industry

Due to equilibria, (or from a reversible reaction), some of the reagents will turn into products as expected, but some of the collected products can turn back into reagents, which may remain in the container of the final collection of the products/"products". So, some of the product was used up to turn into the reagents, which decreases yield and decreases purity. Side reactions could occur, using up some of the reactants, or products, also decreasing yield and decreasing purity. There could be improper filtration so some of the impurities remain, decreasing the purity. The reaction may not have been heated enough, or for long enough, so not as much of the reactants were used, so less product was produced than what could have been, decreasing the yield.