The theme of memory occurs often in the movies. Movies like Memento, 50 First Dates, Eternal Sunshine of the Spotless Mind all deal with the theme of a forgotten past. Without memory we wouldn't be able to learn, without memory, we would be like an amoeba. Without memory we would always be like a child, everyday having to relearn things.
In computational science, a whole class of problems become solvable through the use of memory.
It's memory that allows us to retains joy, to remember the good we did and experienced. However, the flipside to it, is that it also holds our mistakes and regrets.
That's where another class of movies come in, movies like Sliding Doors, Star Trek: The Voyage Home, Groundhog Day, The Time Machine, Back to the Future, Next, Minority Report, Paycheck, 12 Monkeys. These movies deal with the human problem of changing our past decisions or to see into the future to enhance our decision making ability.
A lot of mental problems come from dealing with the past, where we can't accept the past, of what happened, of hurts, of pains, a loved one slipping out of our grasp, a treasure lost, a mistake made. And then there's the future, where we wish we knew what we could do.
Movies like Paycheck, Minority Report demonstrate why the ability to look into the future is so dangerous, too dangerous in fact, because knowing the future means we control others' futures as well--a far too dangerous responsibility for man to hold.
So what is the moral of these stories? In some stories, the protagonist succeeds, in other cases, he realizes that the past cannot be changed no matter what he does.
In Back to the Future Marty changes the past a little and thereby the future as well, but learns to control his tempestuousness. In Next Nicolas Cage's character sees the future and learns to cooperate. In Groundhog Day Phil learns from his mistakes and grows from each repeated day. In Sliding Doors we are privy to two alternate futures but each shares a journey of growth. In 12 Monkeys Bruce Willis's character makes a final sacrifice to try and save the future. In Eternal Sunshine of the Spotless Mind Jim Carrey realizes that his love will overcome the decision to erase his past.
There is one thing in all stories, that must happen, is that either the protagonist grows from his past mistakes, achieves enlightenment and accepts what has happened, or changes in his/her behaviour to prevent repeating the same mistake.