Compared to other species, human beings are certainly endowed with good intelligence, yet unless they are devotees of the Lord, all their thinking is limited within mundane boundaries. Therefore it is impossible for the mundane mind to approach the transcendence. But instead of surrendering to the Supreme Lord or His representative, the empirical philosophers try to explain away as "unmanifest" that which is beyond their mundane minds. This is known as the logic of the frog in the well.
No matter how big a thinker a tiny living entity may be, all his activities are limited by mundane boundaries, just as a frog in the well can never comprehend that such a thing as an ocean exists outside his little domain. He refuses to acknowledge that a mass of water infinitely bigger than his tiny puddle can at all be possible.