History constantly repeats itself, why?

The short answer, we forget about the events in the past, they fade into the back of our memories, it's the way we humans are built, it's neccessary too, because our brain wouldn't be able to cope with having memories always remain in the forefront of our minds.

Why am I writing about this?
When something has happened in the past we most often don't learn enough from it, or at least don't stay committed to any change we vowed to make.

One example, Ricardo Campogiani, a 16 year old boy beaten to death by a group of guys in Stockholm, October 6th 2007. It led to a massive anti-violence demonstration where thousands of people turned up to show solidarity against the violence in society. It was a great accomplishment at the time, but what did it actually achieve? nothing. People unrelated to the victims and perpetrators by now have forgotten all about the demonstration and the urges for a cease to the mindless violence on our streets. From the day Ricardo died until today there will have been other victims just like him, nothing has changed. Laws and policies to ensure a safer society isn't going to come quick either because bureacracy is one of the slowest machinations in society.

Society most of all lacks complete commitment, no follow-through, to learn from history, demonstrations, rallies, celebrity pleas etc, they're in the spotlight at the time, vows are made, everyone nods their head in agreement, that they are changing things by the vows and spoken committments, but when it comes down to it, how much is done? not enough.

How many people like Ricardo need to die before we as a society say enough is enough, mean it, and stand by it. Zero tolerance of violence is quite realistically a utopian dream. Yet, we can do much more than we are doing, come up with new solutions to deal with conflicts, improve safety on the streets with more lamps, citizen patrols etc, educate people more than we are doing at the present about the consequences of violence.

There's a saying, 'time heals all wounds', but if time implies forgetting, it means we're not truly healing. We mustn't forget the past, because it's the only thing we can truly learn from.