The paths of your minds naturally travel in very different directions and you could end up looking at this person as a stranger -- and not an interesting or compelling one. Instead, you tend to view your intellectual differences as a sort of threat to your own point of view. This didn't happen right off; in fact, in the early stages of your relationship, you might even have been attracted to these mental differences, because they seemed so new and intriguing.
But after some time, as you got to know each other better, you realized that your ideas are often incompatible. This person is more intuitive than you are, while you tend to rely more on logic -- and neither of you is able to understand why the other isn't more like you. When arguments erupt and you each take your standard position, there can be no resolution because how can emotion or intuition win out over logic, or vice versa? Neither is inherently more correct or reliable than the other, but you can both spend plenty of time trying to prove that your point of view is, in fact, the more valid one. At base, you are uncomfortable with your partner's leaps of faith and unorthodox ideas, and they're impatient with what they see as your stodgy and unimaginative approach to the world. You have to strike a balance between the two if you want it to work out -- and you have to learn to respect the other's way of doing it.