When we are not focussing, the brain automatically turns on the autopilot. This is the basic state of the brain. In scientific experiments it was be shown, that this state occupies more than 50% of the time. The brain then deals with distractions from the environment that can have an impact on one’s own life. The system looks for evidence of threat. As soon as something threatening is recognized, the body is put into an active state in order to flee or fight. The system avoids dangers and threats.
You can easily notice this condition by closing your eyes and trying not to think about anything. Then your thoughts start to wander and the subconscious is active. It reacts quickly, is sensitive to emotions and thinks short-term. In the course of life, however, our subconscious has also learned some routines and thought patterns that are not helpful (biases, etc.). Often, we are not even aware of this.