Fire will act, regardless of whether handled by an innocent child or by someone well aware of its power. For example, if a field of straw or dry grass is set afire, either by an elderly man who knows the power of fire or by a child who does not, the grass will be burned to ashes. Similarly, one may or may not know the power of chanting the Hare Krishna mantra, but if one chants the holy name he will become free from all sinful reactions. In the Western countries, where the Hare Krishna movement is spreading, learned scholars and other thoughtful men are realizing its effectiveness, the movement is turning hippies addicted to drugs into pure Vaisnavas who voluntarily become servants of Krishna and humanity. Even a few years ago, such hippies did not know the Hare Krishna mantra, but now they are chanting it and becoming pure Vaisnavas. Thus they are becoming free from all sinful activities, such as illicit sex, intoxication, meat-eating and gambling. This is practical proof of the effectiveness of the Hare Krishna movement. One may or may not know the value of chanting the Hare Krishna mantra, but if one somehow or other chants it, he will immediately be purified, just as one who takes a potent medicine will feel its effects, regardless of whether he takes it knowingly or unknowingly.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Sixth Canto, Chapter 02 – Text 18 & 19