The brain is the perceiver, the feeler and the thinker. It is a thought generator and not the controller of it's own thoughts, the power to control its mental activity comes from you and that depends on your self-awareness. It is your job to cultivate self-awareness and through it you can achieve a state of physiological and psychological equilibrium and thus avoid the turmoil of compulsive emotions which inevitably cause confusion, anxiety and stress in you .
Every cell in your body is connected to a nerve, and every nerve is connected to the brain and the brain is influenced by your thought(s) either positively or negatively. Thoughts can be thoughts but you don't have to think them. If you want to think them then choose them carefully. Because every thought that you choose to think with, produces a neurochemical output which interacts with the tissues of your body and affects their functioning either positively or negatively. When the effect of a thought on the body is negative, we don't like it and we react by thinking about it. If you are wise, you could force yourself to change that reaction into a response in order to "Stop and reflect" so that you don't make a mess of your feelings or get into trouble or feel guilty afterwards. Feeling guilty is not good for your health.