The second component of the fitness is weight. A valid (or nearly valid) solution is preferable to another if it has a lower total weight. Calculating the total weight requires much less computation than checking the validity of a solution. Because of this we can determine the quality a solution will have if it turns out to be a valid solution, quickly and independently of checking whether it is, in fact, a valid solution. Knowing the potential quality of a solution can help us decide whether or not to invest the time in checking its validity. If we decide not to evaluate the solution, then it is never added to the population.