The whole idea of a set in stone "system" is unrealistic. Assuming most of us here are fans of Dr Phil, we should go look through his books about how relationships are constantly renegotiated. How many of us can honestly say that having children is EXACTLY how we predicted it would be?
This holds true in the work place, too. When one aspect of my husband's job grows in scope or magnitude (i.e. three toddlers!), he talks to his boss and renegotiates his responsibilities.
ooohh!! It is a beautiful day here in Florida, and my hubby just informed me he has the opportunity to play golf. We negotiated that he would get to golf, and I could get out of dinner duty! See! Everybody's happy!
