Some authors simply don't understand the importance of factual statistics. I see a lot of it in psychology. Your choice as a reader is to close the book, or cha

Some authors simply don't understand the importance of factual statistics. I see a lot of it in psychology. Your choice as a reader is to close the book, or change your frame of reference with regards to the statistics in the entire book. In this case, the author is probably trying to convey that for a lot of people their personalities will change over the course of 30 years such that at the 20 and 50 year mark a minority of ones personality is still present. Don't get me wrong, I hate fake stats, but at least changing _my_ expectations allows me to enjoy more books without zeroing in on what could be a minor issue in a much larger and interesting point.