Why do we always use coefficients for equilibrium constant equations?

For my understanding, with the exception of all the steps of the reaction given, including the rate-determining (slowest) step, that would determine the rate law reaction, the rate law reaction (order of each reactant and the overall reaction order) must be determined experimentally. For an equilibrium constant, the coefficients for the overall formula for the reverse and forward reactions, can be used to put together the equilibrium constant formula?

Is the reason one can use the...

Why do we always use coefficients for equilibrium constant equations?