We are not concerned to hear any rascal. We want to hear Krsna. We are not prepared to hear any rascal, so-called scientists and so-called philosopher, so-called God. No. We are not prepared. Because everyone is rascal. Everyone is full of mistakes, everyone is trying to cheat others, everyone is illusioned, and everyone's senses are imperfect. How he can give knowledge
perfect? That is not possible.

Therefore, we have to select guru. Guru means Krsna. As Arjuna has selected guru, sisyas te 'ham sadhi mam tvam prapannam: [Bg. 2.7] "I am, I become Your sisya, disciple, and I surrender unto You." So to get perfect knowledge, we have to find out Krsna or Krsna's bona fide representative. Then there is perfect knowledge. Then we can become immortal.

(From Srila Prabhupada's talk on Bhagavad-gita 2.15 — London, August 21, 1973)