From J. D. Allen's book Humans in Training:
Past and future do not really exist; they only exist in our minds. Yet they appear to be very real to many people who struggle because they are so focused on the past that they are not able to move beyond it. Others are so stressed out about what might happen in the future that they are not participating in the present. The present is the only time that really exists. The extent to which we live in the past or the future, rather than the present, makes all the difference in the world about the direction our life is taking. Whatever dominates an individual's present thoughts, feelings, decisions, and actions, determines the direction in which their life moves. Why is it that they make rearview mirrors in cars so small? So we can be aware of what is behind, learn from the past, yet remain focused on the here and now and on where we are going.