In this chapter, we've talked about other behavior design patterns as complements to the former chapter, including Strategy, State, Template Method, Observer and Visitor Pattern.
Strategy Pattern is so common and useful that it may appear in a project several times, with different forms. And you might not know you were using Observer Pattern with implementation in a daily framework.
After walking through those patterns, you might find there are many ideas in common behind each pattern. It is worth thinking what's behind them and even letting the outline go in your mind.