There are six principles which we should avoid. They are as follows: eating or accumulating money more than necessary, wasting energy for material gain, talking unnecessarily, following the regulative principles fanatically without any sense, not following the regulative principles, and to become too much greedy and associate with persona non-grata. So as you are serious in the matter of advancement in Krishna Consciousness, you will remember the above instructions given by Rupa Goswami, and you will feel more and more secure in your endeavor.
Letter to Isana das, 23 May, 1969