In Genesis 3:5, the serpent tells Eve “when you eat from [the tree of knowledge] your eyes will be opened, and you will be like God, knowing good and evil.”
Why is it the original sin to know good and evil? Because when we accept that there’s no objective truth and that everybody can decide what their “own truth is,” all kinds of really bad shit begin to happen. When everybody becomes their own little god and tries to bend reality to their own whim, this never ends well for anybody. Because objective reality does exist and it’s very unkind to human delusions of grandeur.
The postmodern mentality that there’s no objective truth, just individual truths that have to be equally respected is a philosophical and practical dead-end. Humanity has known this for at least 5,000 years but then unfortunately started to forget this important fact.
All of the above is a quote from Arestovich’s seminar on the foundations of philosophical thinking. Ukraine suffered enormously because of the world’s embrace of the idea that “everybody’s truth is equally valid” and “whatever you feel is the truth”, so now Ukrainian thinkers are at the forefront of explaining why this mentality is stupid. Thankfully, in Ukraine there’s no stigma on quoting the Bible in intellectual debates, so nobody has to pretend that these ideas are new and have to be defended as some sort of a weird, newfangled quirk.