Study the past to divine the future. --- Confucius
It is hard to argue against a master's pure thought.
Human beings do dwell on the past in order to divine or predict their future.
They do so in work: if I did X,Y, and Z then I should get that promotion.
They do so in relationships: if I did A,B, C with Lady One in the past but that did not work out, if I do X, Y, Z with Lady Two I will have a better relationship with her.
Sometimes, we get trapped in the past. When the "what if" scenarios begin to consume your thinking and reflecting time, you get caught up in the past which freezes the present to cause a fantasized future hope.
If you replace the "what if" with a more proactive, positive "what's next" attitude, then you are living in the present with a better outlook for the future.
This is best observed when people date and break up. Depending on how sudden or blindsided the break was, two things can happen. One, some can hide in the past (the good memories) to the point where they obsessive chase to get their former lover back in the future. Their future is a time loop of disillusion and rejection. Failure. Two, some can let go of the past to the point where they can move on to find a better friend and lover. Their future is moving forward into the future with confidence and new awareness based upon experience. Progress.
The perfect character study for this behavior pattern was John Locke.
Locke carried with him additional baggage from his childhood abandonment issues, and added more baggage with each failed relationship. His past haunted his present and clouded his future.
His obsession with his con man father, even after he conned him out of a kidney, destroyed the best relationship he ever had with another person, Helen.
In the real world, he found a woman who loved him for who he was, but since Locke had so much personal baggage unresolved in his mind (that he could not love himself enough to be loved), he effectively destroyed the best chance he had for happiness.
And even if one considers the sideways world as Locke's "fantasy" future to try to get Helen back after their final break up on the mainland (island time frame), that did not work out either since Locke ended the series alone in the church.
Human beings try to project future happiness upon themselves. But just fantasizing about it will not make it happen. Action speaks louder than words. Action also speaks more to obtaining a new future than just thinking about it.
Locke never tried to replace Helen in his life. And that was his down fall. His failing. His past ruining his future because once he realized that Helen was very good to him (and for him), it was too late. He could have went back into the dating pool to find a new Helen (learn from his past mistakes) but he was too afraid. He envisioned himself as some grand outback warrior, but that was pure fantasy clouding his judgment and detouring him from real, tangible goals.
And this trap is what makes people have lonely lives.