The general idea is to change direction aggressively when getting an inside groundstroke, right? It seems like most inside groundstrokes will be towards the center of the court, and the book reccomends to hit perpendicular to the base line when changing direction (the 90 degree COD). This means if you change direction on an inside groundstroke that's in the center of the court, you'll be hitting it to the center of your opponent's side. To me that sounds like you're just giving your opponent an inside groundstroke to attack you back with. Am I missing something?