Your marriage is fine, right? Sure, there are showdowns over who unloads more dishes, and some simmering discontent over who drives more car pools, cleans more dust bunnies, and keeps the social wheels of your existence greased. The sex is good, though you can't remember when you last had it. Come to think of it, you're plagued by a nagging sense that marriage used to be so much more fun. Marriage can be a mysterious, often irrational business. But the key, propose Paula Szuchman and Jenny Anderson in this incomparable and engaging book, is to think like an economist. We all have limited...