Live In The Present
For many people, sadness and suffering is not a result of present experiences. Rather it is pain caused by regretting and resenting the past, or worrying about the future.
Living in the present saves you from needless emotional pain. Additionally, keeping one's mind on the present is necessary to concentrate on the important tasks of the day.
Be aware of your failure to keep your mind on the present. This will help increase your ability to do so.