The Past, The Present & The Future

We always hear and see this phrase "The Past, The Present & The Future".
Ever really stop to think of the meaning of the phrase?
Can the three really exists together in harmony?

There are both good and bad memories in the Past which had been 'sealed'.
The thing is why does one always think of the Past?
Is it because the Present is not good enough?
Or it's just that she simply can't see the Future?

If one can't let go of the Past,
Present will be tough and
there might not be Future.