In chemical equilibrium the equilibrium constant accounts for a measure of the direction of the undergoing chemical reaction; in other words, the equilibrium constant help us to know whether a chemical reaction moves rightwards or leftwards. In such a way, if we say that the reactants are favored, the inverse reaction (leftwards movement) is looked for, in this manner, the equilibrium constant must have a value less than 1 based on the law of mass action for a given reaction A⇄B:
Therefore, if K<1 the concentration of A will be greater, favoring the formation of reactants.