By Stan Tatkin // I watched the popular TV show Madam Secretary, and there was a moment when the central figure got a mini lecture from a Nobel laureate mathematician about negotiations. The character stated that the key to getting disparate parties to agree on peace is to illuminate their interdependence. I won’t say I got the basic idea for this blog from the TV show, but I was inspired to write after watching it. Interdependence means, in the case of couples, that each partner has a stake in something. We could say childrearing is one such shared investment, although having a child is not sufficient to keep couples together. Just look at the stats. Because many partners do not function securely together to begin with, they tend to become increasingly insecure when they add children. They resort to childrearing as a separate endeavor and not as lovers collaborating in a family enterprise. The demise of their relationship should not be a surprising outcome. But there is another common tie that should bind partners together: …