Do you have a book for parents raising two teenager girls?, a guy said. He was in the next aisle at a bookstore. I was looking for some Christmas presents. I had on my hands Clear Thinking and The Cat Who Saved Books. I was looking for a third book to take advantage of the month’s promotion. The cheapest of the three was free. The guy kept walking the aisles. An employee started to recommend titles: Think and Grow Rich, The 5:00 Club… Then his daughter said, “I’ve seen this book…I don’t know the title, but its cover is a...