When you live in the past, you lose the present.
It's not easy - not at all - to let go of many aspects of the past (and the bitterness that accompanies some of those aspects), since they contributed to the present in real and tangible ways - and it's not healthy to let go of the past in lots of ways, but it's really important not to live in or obsess about the past (whether that is one's own past or a communal past). All we have is the present, and the only healthy objective is to make the best on-going present possible. Living in the past is perhaps the best way to not allow that to happen - to limit in a very real way the growth that is possible by letting go of the past.
Again, this is applicable to lots of aspects of life, and I am not going to try to make a list. How it applies will vary from person to person, so, as the title says, this simply is something to consider.