The book, unfortunately, promotes the widely believed myth that 50% of all marriages end in divorce. Untrue.
The statistic came out of a feminist group a few years ago. They divided the total number of marriages in a year by the total number of divorces: 50%.
However, the divorces were cumulative. So the marriages (for that single year) were divided by divorces due to marriages FOR ALL PREVIOUS YEARS.
So everyone married in say 1994 was compared to all the divorced marriages from say 1940 to 1994. Good example of how to lie with statistics.
When you compare apples and apples (say the total number married in 1960 compared to how many of the SAME PEOPLE were divorced by 1994, you get something like 6%)
But some like the inflated false number better. They want to redefine what is normal (divorce can't be abnormal if more than half do it!) thus make it the easy path to take.
Everyone repeats the 50% number, it's false, and a shame this book fell for it too.