It's easy to remember the past, easy to stress about the future and hard to focus on the present. It's easy to reflect on past memories, both good and bad, and realize things could always be better or worse. It's stressful to think about the future and how things may or may not play out; However, why is it so difficult to just focus on the present?
Nostalgia seems like it can take over at every blink of the eye. It takes over the mind with thoughts of past friendships, memories, successes and failures, and it almost always leaves with the "What if?" question. The past is easy to go back to because it's already happened. It's an easy place the mind often goes to when it wants to escape from stress.
On the other hand, however, the mind spends a lot of time dwelling on the future, which in turn, creates stress. It's like a never ending cycle. I'll often find myself day-dreaming away about what could be, would be and should be, and I become consumed with future thoughts that do nothing but stress me out because I believe the only way things can unfold correctly is the way in which I think think them up (stress about) in my head. Focusing on the future leads to stress, and stress leads to nostalgia. The future and the past are not where we should be; we should be in the present.
Staying in the present is easier than said than done. Sure, it's easy to physically be somewhere, but how much harder is it to mentally be there? It's much easier to check out than it is to check in and focus. When's the last time you were fully invested into a conversation without wondering what was for lunch, how many missed texts you had or whether or not the person you're talking to is almost finished talking?
Dwelling on the past and stressing about the future rob the present. It's not wrong to reminisce on old memories, but don't do it so much that you miss the opportunities to make new ones. With that in mind, don't get so worked up about the future that you forget to take care of the present so the future can happen.
"Wherever you are, be all there."
-Cliff
Cliff's Note: Don't be so nostolgic that it robs you of future opportunites to be nostolgic.