A.C. BHAKTIVEDANTA SWAMI PRABHUPADA – Having acquired a good sitting place in a secluded environment, the yogi begins to purify the atma—body, mind and soul. The yogi should not think, “Now I will try to achieve some wonderful powers.” Sometimes yogis do attain certain siddhis, or powers, but these are not the purpose of yoga, and real yogis do not exhibit them. The real yogi thinks, “I am now contaminated by this material atmosphere, so now I must purify myself.”
We can quickly see that controlling the mind and body is not such an easy thing and that we cannot control them as easily as we can go to the store and purchase something. But Krishna indicates that these rules can be easily followed when we are in Krishna consciousness.