I think you can figure this out on your own.
Imagine you are on a journey. Most of the way, you are on long, straight, well-paved, even roads. Sometimes, however, the road is not very well-paved. It's rough. There may even be rocks in the road. How comfortable is that part of your journey, compared to when you get back on the nice, smooth road again?
Now apply that to a relationship. It doesn't require "strong arguments," but perhaps areas of disagreement or just a desire to do different things for a while. (On the other hand, it could be strong arguments, etc.)
Note that "we hit a rough patch" is the same metaphor for "we hit a rocky a patch" and you can use "area" instead of "patch."