Upanishads:~ Fools dwelling in darkness, but thinking they wise and erudite, go round and round, by various tortuous paths, like the blind led by the blind. (Upanishads Nikilanada - Ch II-5 P-14)
The seeker has to overcome all the obstacles in pursuit of truth on his own. They are so many scholars who mastered philosophy. It is impossible to acquire Self-knowledge by studying Vedas and theoretical philosophy. Because their preaching is based on spirit and practices is based on ego (you).
Katha Upanishad: ~ This Atman cannot be attained by the study of the Vedas, or by intelligence, or by much hearing of sacred books. It is attained by him alone whom It chooses. To such a one Atman reveals Its own form. (Ch-II -23-P-20)
For the same reason Sage Sri, Raman Maharishi said fortunate are the one who do not lose themselves in the labyrinths of philosophy. Bhagwan says: Take Vedanta, for instance: it speaks of 15 pranas the names and functions of it which the student is asked to commit memory. Will it not be sufficient if he thought only one prana does the whole work of maintaining the body? Again the antakaran is said to think, to desire, to will, to reason etc. Why all these details? Has anyone seen antakarana, or all these pranas? Do they really exist? They are conceptual divisions invented by teachers of philosophy by their excessive analysis. Where do all these concepts end? Why should confusion created and then explained away? Fortunate is the man who does not lose himself in the labyrinths of philosophy, but goes straight to the source from which they all arise. (GURU RAMANA .By S.S Cohen -vii Danger of philosophy-Page -58-59)
It is very difficult to talk to people about ultimate truth or Brahman because everyone thinks he knows the ultimate truth or Brahman. This- I know business is dangerous. And whatever his reached conclusion is secondhand stuff. Therefore, accepting accumulated knowledge without verification will lead the seekers to hallucinated realization based on the ego. One may have some flashes of truth when someone tries to indicate it through fewer words. But it takes nearer to the truth, not the realization of truth.
Upanishad's say :~ "He who thinks he knows, does not know." This means that to know anything implies a second, an object of knowledge, hence duality, i.e. no Gnana.
Tripura Rahasya, 18: 89:~ Second-hand knowledge of the Self-gathered from books or Gurus can never emancipate a man until its truth is rightly investigated and applied; only direct realization will do that. Realise yourself, turning the mind inward.