Mental peace is so important because it can help you remain calm in the face of distress by easing feelings of anxiety, worry, and overwhelm. Without peace of mind, you might eventually begin to notice symptoms of anxiety and stress, including sleep disturbances. aches and pains. : a feeling of being safe or protected Installing a security system in your home will give you greater peace of mind. A relaxed and calm outlook can help you navigate life’s often-turbulent waters more smoothly.