"My dear Lord, devotional service unto You is the best path for self-realization. If someone gives up that path and engages in the cultivation of knowledge or in speculation, he will simply undergo a troublesome process and will not achieve his desired results. Just as a person who beats an empty husk of wheat cannot get grain, one who engages simply in speculative knowledge cannot achieve the desired result of self-realization. His only gain is trouble."
In the Bhagavad-gītā (7.14) it is stated that material nature is so strong that it can be surmounted only by those living entities who surrender unto the lotus feet of Kṛṣṇa. Only they can cross the ocean of material existence. When a living entity forgets that he is eternally the servitor of Kṛṣṇa, that forgetfulness causes his bondage in conditioned life and his attraction for the material energy. Indeed, that attraction is the shackle of the material energy.