Man's thinking is volitional. It requires choice. Thinking is not automatic. The use of reason to integrate percepts into knowledge, or knowledge into more abstract knowledge, does not happen on it's own. It is a process that takes effort. Man must focus on what he is doing. He must act.

Focus applies to perception since man can choose to ignore his senses. He can focus on something else. When we day dream, we often ignore our immediate surroundings. Additionally, there are degrees of focus. We can look at a friend and recognize her, but we can focus even more on particular features, such as her eyes or hair.

Focus is especially important in the realm of ideas. Since man's entire base of knowledge, including one's memories, is readily available his choices of thought are wide open. The mind could easily wonder from topic to topic like a bored T.V. watcher with a remote control. Focus is required to stay on a topic, and think deeply.