Humans are a forgetful species. From natural disasters to political upheaval to pandemics like the one we’re in now, we forget all the bad times we should have remembered and learned from- that is, unless we not only lived it, but were directly affected by it.
Take for example racism. It is a long-standing problem in the US- it’s been around for centuries, actually- and we’ve had plenty of lessons on equality, but many people don’t learn. Take for example police brutality toward African-American people, and normal citizens calling the police on them for just living their lives as usual (think of the killings by police- the very people who are supposed to protect- and the woman who called the police on a man who only wanted her to leash her dog, as per the rules). If humanity has learned anything from the era of slavery, activists like MLK, and and a war, this shouldn’t be happening.
But humanity hasn’t learned; rather, it has forgotten- or it has never known at all. Presumably people forget because they weren’t/aren’t directly, personally affected by the problem at hand, so they know little of it. But people who were directly affected by the problem might forget because they hold memories of it too painful to think about. And then there are people who have never known the problem at all, never lived through it, were never affected by it, and they either choose to try and understand and help or remain ignorant of all the lessons they should learn and say things that hurt and never help at all (one notable example is currently in a powerful position and has said things like “the China virus”, leading to violence against Asian-American people. This stands independent of my political views and I will say naught about them).
In conclusion, humanity forgets because of pain, distance, or sheer lack of empathy, which is the real problem behind many of our problems- racism, bigotry, violence, etc. If people would try, really try, to feel what it is to be in another’s position, maybe these problems wouldn’t be so severe. Maybe some of them need never have existed at all. Maybe if everyone read To Kill A Mockingbird and took a leaf out of Atticus Finch’s book, the world would be a better place- but sadly (sometimes), fictional people are- well, fictional.