Why "other things being same" phrase associated to law of demand?

Law of demand explains the relationship between quantity demanded of a commodity and its price only. But other factors such as price of related goods, income and taste and preference of the consumer etc. are bound to change sooner or later. That's why it's assumed that the factors other than own price of the commodity are constant, so that these don't effect the demand curve while analysing the "quantity demanded-price" relationship.