See also : Nietzsche
Quora Answer : Why did the West end up falling in the nihilism of postmodernism?
What most people you see complaining about nihilism and postmodernism don't understand is that these are the end results of a process of rigorous destructive testing of ideas in the Western cannon of thought.
Modern Western philosophy can be thought of as starting with Descartes, who tried to put philosophy on a more rigorous and trustworthy basis by demanding that people should only believe things that they had good reason to believe. Rather than just speculate randomly as philosophers of the past had done.
Western philosophers then spent several hundred years trying find "good reasons" for the things they believed. And accepting that they shouldn't cling on to beliefs when they couldn't find them.
They ran through all the obvious stuff. And the obvious objections.
You could believe your own eyes, right? Except maybe not if you didn't know you were dreaming or hallucinating or being tricked.
Well, your memory was good. Except when you forgot. Or misremembered.
But surely sound reasoning was reliable? After all, Descartes had proved that God existed by reason alone. Although it was kind of weird that when the great thinkers like Leibniz and Spinoza tried to reason about the kind of world we lived in, the picture they came up with was full of the strangest things; and if they were right, then WTF, and if they were wrong, then reason wasn't so infallible.
The more philosophers interrogated their ideas, the more certainty slipped away.
The more they thought, the better they got at finding the awkward edge-cases and counter-examples to all the "common sense" beliefs that had seemed so unproblematic before they started.
In the 19th century, historians were discovering more and more about how differently people in the past had thought and behaved, and how much European values had changed between the Greeks and Romans, and the modern times. How could you believe your morals were eternal absolutes when the great figures of antiquity didn't follow them?
Scientists kept delivering ever more counter-intuitive and problematic information. Galileo and Newton removed the Earth from the centre of the universe and sent it flying around the sun. Darwin demolished the idea of human "specialness", making humanity just one more animal with no justification to claim greater morality, values or wisdom than a beetle. Psychologists and sociologists eagerly followed, showing just how mechanical and arbitrary and constrained human mentality was. Einstein's Relativity and Quantum Physics undermined even more of what seemed so certain.
The final nail in the coffin of pretensions for Western thinkers, were the disasters of the first and second world wars. Where European civilization turned on itself with utter ferocious barbarity killing 50 million people. By the time you'd seen the horrors of the trenches, and the gas chambers, and the nuclear bomb, the idea of Western "civilization" as having a claim to moral superiority over other human cultures was a sick joke. No culture in history had spilled so much blood or been so careless of human life, or blind to the consequences of its actions as the children of Enlightenment liberalism.
What "certainties" would you be willing to bet on after Einstein had shown that even time and space were not absolute fixed geometries, after "solid" material was revealed as being made of tiny particles, which were also "waves" that couldn't, even in theory, be localized at any particular place. And that human thinking could be predicted by neuroscientists and emulated by machines?
Basically the only people who can and do believe in absolute values and firm unassailable foundations of knowledge, haven't really been paying attention. Or are the kind of people who have been sticking their fingers in their ears singing "La la la, I can't hear you", when scientists give their latest findings, and when Wittgenstein shows them how problematic it is to know what +2 "really means".
Nihilism and post-modernism are not what you think they are. They aren't "a belief in nothing". Or an absence of morals or absence of rationality. They aren't Sophomoric posturing.
They are the the last surviving ways of keeping intellectual life going and finding a way forward, when all the wrong stuff, all the pretension and self-delusion has been stripped away by a rigorous fire of logic and sceptical enquiry.
You may be such a special snowflake that you believe that your culture and ideas and moral values are superior to everyone else's. Are more right. And more good. And more beautiful. And more solid. But facts, as someone famously said, don't give a flying fuck about your feelings.
And hell knows philosophers have tried to find objective justifications for a belief in God. In objective morality. In logic. In scientific observation. In artistic excellence. Etc.
And they have all, ultimately, failed to provide good reasons for any of these.
The only thing that has stood up ... at the end ... is the belief in "power". That ultimately our beliefs are the product of a kind of "might makes true". And that's just because it's also an empty tautology; what is "power" in this sense except the ability to make people believe things and see the world a particular way?
Samuel Johnson is celebrated as providing one of the great responses to idealism (the belief that the world is made of nothing but ideas), when he kicked a stone and said "I refute it, thus". Sadly, wonderful as this response is, it is merely yet another argument from power.
Every single attempt to deny the sceptical philosophers boils down to "I refuse to believe it". Again, it's nothing but an argument that "I have power over my beliefs and I refuse to let you change mine" Everyone who hates post-modernism and posts against it on the internet is actually using the very thing that they claim to decry.
There really is no escape.
The West hasn't "fallen" into nihilism and post-modernism. It has "achieved" nihilism and post-modernism, by succeeding so well at the game of rigorous intellectual enquiry.
 Well, there is also Popper's "critical rationalism" which I'm a fan of, but which is too complicated to go into here.