People internalize traumatic events when their brains cannot resolve the issue. The gov does not help a country's healing by locking away the truth for decades or forever. This triggers a lot of conspiracy stories, which in themselves can increase and prolong suffering.
The hardest lesson to learn is all of us have good and evil inside. All of us are capable of committing horrible atrocities. When someone does, that gives a glimpse to how wicked our own evil inside can be. Once you realize we all have this flaw, it's much easier for the brain to process any trauma in the future.