[A water user could have wind too, and if they were exceptionally lucky, could even have lightning. A fire user could more easily use lightning than a water user ever could, and if they were fortunate, they might also wield earth. The same holds true for earth attributes: they could use fire more easily than water or wind.
[Many powerful people possess all attributes in some capacity, but it's always a matter of percentages—which one dominates and pulls the others along. Having a high percentage in fire will naturally attract more lightning and earth, but it will suppress water and wind almost entirely.
