Landlubbers are accustomed to momentum (p = mv) behaving in a certain way instinctively from years of experience, where the heavier something is, the more frictional force against it from the ground, and therefore the mass behaves a certain way. This breaks down once the expected friction changes a lot, e.g. trying to stop a moving car or, like you said, a boat in water. I'd imagine it's the same thing in space, where a slowly-moving but massive object would surprise someone at their inability to stop it.
