We read in Holy Scripture: "Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof." (Matthew 6: 34). The whole point of this esteemed wisdom is to help us to remember that each of us should make it our point to stay focused upon the here and now, rather than dwell upon the past, which cannot be changed; nor upon the future, which cannot be known for a certainty.
While it is important to own what we have done in our past actions, that recognition should be primarily utilized so as to improve our behavior and demeanor in the present, as well as to take to heart those lessons so learned. On the other hand, many people, spend an inordinate amount of time, worrying about the future, and thereby that constant worry, affects them in a negative way in the present, of which, many of those things that we are prone to worry about, never even come to pass, or if they do, such an event is usually not nearly as catastrophic as previously feared.
This doesn't indicate that we shouldn't plan for the future, or that we shouldn't have goals that we endeavor to work towards, but rather this indicates that in order to achieve anything of substance, requires that such can only be accomplished by that which is so done in the ever present, and as long as we stay focused, driven, and on the straight and narrow, so that we thereby keep our ear always to the grindstone, then the efforts that we put forth each day will ultimately bring us closer to that which we desire strongly for and yearn for. After all, we do not simply become what we what to be, in a single day, but we do get there, day-by-day, as long as we keep our nerve, our concentration, and our purpose clearly in our mind and in our deeds, and endeavor that we shall never give up, daily.
So too, many people spend way too much time, second guessing themselves, and constantly will not let go of negative thoughts, and perceived negative outcomes; without seeming to understand that the way to live a successful life has a lot more to do with taking the time to measure that which needs to be measured, and if necessary doing such twice or even more, before thereby making the cut, which thereby represents the visible result of the preliminary thoughtful work so accomplished, beforehand. In other words, to overcome worry, one needs to be more diligent about addressing daily that which should be addressed in order to achieve or to have that good chance of success, thereof.
So then, there are only twenty-four hours in a given day, of which each of us has mandatory responsibilities that must be dealt with constructively on that day; so that when provided with the opportunity to think and to contemplate, it behooves us to concentrate on that which is the most important issue of that day, so that we can best tackle and overcome that which is right in front of us, and thereby not worry about that which is not, and may not ever be.