Briefly explain why an unbalanced chemical equation cannot fully describe a reaction?

From the conservation of mass, matter is not created nor destroyed. So ponder it this way, for example I put one piece of toast in a toaster, but when it is done I had two pieces, that makes no sense right? Same thing with a chemical reaction but in molecular terms, all things must stay constant. If you put a convinced amount you have to get that quantity back, not less or not more in broad terms.