Self-Knowledge or Brahma Gnana or Atma Gnana can be acquired by anyone --be he criminal or a person from any walk of life -if he will only pursue it to the end, for he will rise by stages until he reaches the level of understanding non-causality, when the highest stage will open before him. Only his own dullness of intelligence can prevent him from attaining non dual wisdom.
The most advanced man is he who exercises his rational thinking when desires or attractions present themselves whereas the least advanced is unable or unwilling to distinguish between primitive desires which arise from his unconscious and the paths laid down for him by his reason.
One must give some time to reflection upon this inquiry, and if he cannot find the time, if his mind is too distracted by activities or worries then he must go to yoga or meditation and get peace alone.
For the seeker must direct the whole of his attention, his whole mind, to the subject of inquiry and reasoning on the true base. Discrimination means reasoning or inquiry.
Seeker of truth should not be disheartened, try over and over again. When he sees that authoritarianism does not give him truth, he goes further. He must have the determination to get at it. Experience tells him that every time he attempt, he progresses.
Non dual Truth may be as bitter as poison, but he must like it as nectar. Those who cannot do this are unfit for self-knowledge.
The right kind of seeker of truth will accept and search for truth whether it brings bitterness or sweetness, whatever it tastes like, for its own sake. He must be prepared to find God as impersonal, and to lose his own individuality for the sake of non-dual truth.