Time dominates our lives. The past, the present, and the future are the three most important aspects of anyone's existence. Although the past, present, and future may seem like three separate entities, it can also be said that the past is present because of its strong influence on our dynamic personalities. The past is present because of the way it shapes our personality and changes our relations with others. The past is the most important aspect of our lives because of the way it dictates everything.
The past has the power to change who we are. Recently, I watched the DreamWorks classic, Kung Fu Panda, and was surprised to hear the allegedly "wise" character Oogway say "yesterday is history, tomorrow is a mystery, but today is a gift. That is why it is called the 'present'" (Kung Fu Panda), which he said when the protagonist felt that he was not cut out to be a kung fu warrior. I consider this to be one of the main flaws of the movie, as a fat, lazy panda is never going to master kung fu in a matter of days judging by his previous lifestyle. This is a perfect example of why the past can (and in this case, should) set limits on what we can do in the present.
Human relationships dwell on the past. We naturally think of people as how we remember them. This is why any past interactions will shape the way we handle any future reactions with the same people. Friendships and even hatred are based on how we have interacted with our friends and foes in the past. It is hard for us to throw away these fragments of the past, which is why many relationships last for so long.
The past gives us a familiarity that we like to dwell on. With the past come schedule, routine, and repetition, and even from birth we learn and are most comfortable with this repetition. From the past we are able to gain an understanding of the present and the future by relating it to something that is familiar to us. This shows that the past influences how we see the present as we are able to relive the past or choose not to relive it based on our previous experiences. Because the past has such a strong effect on everything we know, one could easily argue that the past is present.