While growing up, I always looked forward to the debut of new cars because the designs would change every year. However the European models would not change drastically. Unlike the US manufacturers, they would evolve over a few years whether it be design, safety enhancements or the latest gadgets.
It appears to me that leadership has taken on some of those traits. I searched Amazon Books and found approximately 375,000 titles listed on the subject of leadership. Did the great leaders of yesteryear have to update their skills yearly with the publication of a new book.