As long as the human kind exists there was a seeking for something more, something transcendental. Seeking to find the meaning of life and to end human suffering. From gods of sun, rain and wind all the way to modern "there is no you" ideas.
And from time to time there was someone who appeared to have found it, and his message was somehow brought on to further generations. Most often it was misunderstood and a modern religion formed. Religion took some of the concepts and used them to serve its own purpose.
In some parts of the world quite elaborate mystic schools appeared and it was not based in concepts but more on proof and failure, what worked and what didn't work so much to end human suffering as quickly as possible. In my opinion, such systems would be sufi's sacred enneagram teachings and traditional advaita vedanta. It was a system where a sincere spiritual seeker gave up his life completely in order to find a teacher. Then he would sit with the teacher for a long long time until he would "become" the same as the teacher and until all his doubts were cleared up. Those systems have been working for thousands of years and people were waking up from their trance od suffering.
Ten or twenty years ago one teacher in the west appeared who started speaking about how "this" is always here and there is no "you" to find it and every attempt to find it only strengthens the idea of "you". And so the modern neo-advaita movement formed.
And it is the truth what this teacher was speaking, same statements can be found in texts like Ribhu gita, Ashtavakra gita and so on...but those texts were locked and sincere spiritual seekers were allowed to read them only after decades of spiritual practice or so...and once they read them, they instantly became realised because their minds were so purified by the spiritual practices they performed.
And those scriptures were locked for a reason. It was well know that if the seeker was unripe, the ego would hijack the teachings and the consequence of that is well known and pretty obvious. I can remember myself coming from these modern meetings and behaving like a fool, claiming that nothing matters and I don't exist at all. Perhaps sometimes we have to learn from your own mistakes also...
When it comes to spiritual liberation, honesty is the key. Telling the truth about what is happening is the beginning and the end.....