This isn't very easy to answer. I'm lucky in the sense that I didn't go through the worst experiences human beings have gone through. There are many worst case scenarios, long periods of torture, sexual violence, war, genocide, which some unfortunate beings had to experience. The worst cases of sadism, or predators who ruin your life, or just random bad luck with health which ensures a life of horrible pain and isolation. That's our world. Or even where people were lucky, had great lives, built the relationships of dreams, but then you their kids or partner or family in some really sickening way. None of that happened to me(yet), it was more generic. I got to experience several peak human experiences. I'm very grateful for that. There was still lots of abuse and pain and negative experiences. It was despite constant struggle and confusion that I stumbled into those peak human experiences.
I guess it's just very difficult to get over the egocentrism of one's potential vs. one's actual position/mobility in life. In that sense life feels deeply unfair-- when you know how much more was possible, or your values just don't match with the sorts of things the world rewards. Some people just find success and it's through luck, ultimately, everything in this world is luck and that's inherently unfair. If you know this, then the world will only seem rigged, and this will grate at you constantly insofar as you're unable to get over it.
It's hard to put a number on this, so I won't. It just feels like I was robbed by a continuous stream of bad luck, which is true for most people. You don't have to be one of the unluckiest people to have ever lived to still be very unlucky in this world. Most people born here really just seem like cases of human sacrifice more than anything else.