From author's own experience and observing other couples

He noticed one big source of conflict with couples who decide to hitch together, presumably for life. Many relationships fall apart. The author noticed that a key reason for this conflict, is that a lot of these couples are incompatible to begin with. When such mates decide to commit themselves to a joint life, it is like trying to fit a square peg into a round hole.

The author studied the problem and decided to help future couples select compatible mates, before they make a lifetime commitment. The selected mate would be Next of Kin, as the book title states. The subtitle would then be How to Pick a Compatible Mate.