Perhaps one reason why there is a difference in attitude between both husband and wife is to show the countervailing forces that each embody in the course of the relationship. There is a very odd and off symmetry that transpires between both. When Lady Macbeth is eager to embrace moral evil and depravity, Macbeth seems to demonstrate reticence. When he is willing to plunge into the depths of moral transgression, she is hesitant. In their differences, Shakespeare explores the condition of married couples where there is constant difference and lack of common ground. The push force in one matches the pull force in the other.
The interesting element that comes out of this is that there is never a point in the drama where their differences can be overcome. When Macbeth begins his descent into that which is evil, Lady Macbeth has already started the process of moving away from what she now knows as evil. The difference in attitude between both husband and wife reveals a fundamental disconnect that is never overcome in their relationship. There is a dynamic present that the differences featured in both become a whole. Yet, there is also a rather sad reality that their differences will never be able to be overcome. In this, the differences in attitude between both makes them out to be passing ships in the night more than a married couple. It might be for this reason that upon learning of his wife's death, Macbeth is only able to explain why there is no meaning to existence. The reality of the cost of their differences becomes clear at this point in the narrative.