A Spanish mathematician crunches the numbers on successful relationships:
The results of the mathematical analysis showed when both members of union are similar emotionally they have an “optimal effort policy,” which results in a happy, long-lasting relationship. The policy can break down if there is a tendency to reduce the effort because maintaining it causes discomfort, or because a lower degree of effort results in instability. Paradoxically, according to the second law model, a union everyone hopes will last forever is likely break up, a feature Rey calls the “failure paradox”.
According to the model, successful long-term relationships are those with the most tolerable gap between the amount of effort that would be regarded by the couple as optimal and the effort actually required to keep the relationship happy. The mathematical model also implies that when no effort is put in the relationship can easily deteriorate.