Data in classes can sometimes represent missing objects; Chapter 8 considers this problem.
Chapter 9 looks at the balance of responsibility between superclasses and subclasses, while Chapter 10 goes on to consider the balance of responsibility between other classes. The smells in Chapter 10 must sometimes trade off against each other as we decide how best to connect objects.
Some duplication becomes most obvious when you try to change things, as you will see in Chapter 11. Chapter 12 closes out this section by looking at some challenges in using library classes.