When we are children we are in a state of innocence, because we lack experience we also lack knowledge about the world. You don't know that you could have better parents that would treat you better, you don't know that there are people starving in the world or war etc.
And because of your lack of knowledge for the most part you are satisfied with what you have. As you mature you learn more and more about the world around you, and all the negative aspects of life, this will generally create discontent in the young adult.
I think this is why it is so common for young people to party and do a lot of drugs, they are in a lot of existential pain caused by the knowledge they just learned.
Initially the only way it makes sense to be in the world is to try to fix it. This is another thing young adults have in common, they wan't to change the world, because the are terrified of it.
It might seem an altruistic pursuit, though the true motivation for people who act in such a way is the terror that plagues them. They want to change the people around them to control their anxiety not necessarily because they are altruistic.
After a series of failed attempts most people will give up, after all the world it is broken by design, there is nothing that can be fixed. Because it is impossible to get rid of polarity, good people become bad if gain access to power, there will always be some evil in the world.
The most miserable people I know are those who attempt to change the world, and that it is because they are simply attempting to do the impossible.
In this attempt to fix the unfix-able, you can fall in some pretty bad traps, because your priority is to change people not help them, so it is easy to justify sacrificing someone for the grater cause.
Some people who tried to change the world through the course of history are some of the most evil people who ever lived and created some of the most dangerous ideologies.
After someone gives up on trying to change the world, there are two possible ways you could end up in. One is to become nihilist to reject all moral standard because it is impossible to stop the cycle of corruption. And the other option is to learn to accept the world for what it is.