The 1st written references to the concept of guru are found in the earliest Vedic texts (~1500 bce) which became the basis of Hinduism. Sages scrivening wisdom doubtlessly date to the earliest writings; an echo of what had been orally passed down through generations in prehistory. Knowledge may be lost in social chaos, but the sagacity that comes from realization is individually received, and so transcends time and place.
It is not that you knew what you are and then you have forgotten. Once you know, you cannot forget. Ignorance has no beginning, but it can have an end.
The world is full of contradictions, hence your search for harmony and peace. These you cannot find in the world, for the world is the child of chaos. It is your restlessness that causes chaos. ~ Nisargadatta Maharaj