while this may appear to be a case of a domineering wife controlling a weak man, it actually represents a mutual interplay of fantasy and control. the wife does not and cannot really control the amount of diet coke the man drinks in a day. if he wanted to drink more, she very likely would be unable to physically restrain him in order to stop him from doing so (picture this in your head NOW). what is likely happening, is that the man himself does not want to drink more than one diet coke per day. he has a short-term desire to drink an infinite amount of diet coke, which he has little control over. he idealizes himself as a man who can control how much diet coke that he drinks, and the distance between his idealized self and his current self generates psychic tension. by externalizing the locus of control to his wife, he frees himself from his own judgment and expectations, and releases himself from the burden of self-imposed restraint. he offers the control to his wife, like a gift, and she gladly accepts. she enjoys the fantasy of having control over his diet coke habits, and he enjoys the relief the externalized locus of control brings to him. this represents a mutual dynamic in which both parties are healthy and happy, and neither party is truly controlling the other. in addition to that, I'm gay.