from going back to school to get my bachelors in marriage and family studies, it would be that Dr. John Gottman is a freaking genius. I think that everyone of my classes, even my communications class, mentions his book "Seven Principles for Making Marriage Work." In my Family 300 class, it is one of my text books.
If your marriage needs any kind of help, even if you think it is strong, get this book. It has some great activities that will strengthen your marriage. If you know anyone getting married, this would be a great gift. This man is brilliant. He has done so much research, it is so interesting. You should Google some of his experiments. It is super interesting. Anyway, I guess that is my spiel for now.
You really should get this book. It is the best $15 you can spend.