Due to four imperfections in us, we can never deliver perfect knowledge
A living being who lives in the mundane world has four defects: (1) he is certain to commit mistakes; (2) he is subject to illusion; (3) he has a propensity to cheat others; and (4) his senses are imperfect. No one with these four imperfections can deliver perfect knowledge.
– Srila Prabhupada, Sri Isopanishad Mantra 1