The human mind is a public place open on all sides, and in this public place, things come, go, cross from all directions; and some settle there and these are not always the best. And there, to obtain control over that multitude is the most difficult of all controls. Try to control the thought coming into your mind, you will see.
Simply, you will see to what a degree you have to be watchful, like a sentinel, with the eyes of the mind wide open, and then keep an extremely clear vision of the ideas which conform to your aspirations and those which do not. And you must police at every minute that public place where roads from all sides meet, so that all passers-by do not rush in. It is a big job.
Then, don’t forget that even if you make sincere efforts, it is not in a day, not in a month, not in a year that you will reach the end of all these difficulties. When one begins, one must begin with an unshakable patience. One must say, “Even if it takes fifty years, even if it takes a hundred years, even if it takes several lives, what I want to accomplish, I shall accomplish.”
Once you have decided upon this, once you are quite conscious that it is so and that the goal is worth the trouble of a constant and sustained effort, you may begin.
Ref: Questions and Answers (1950-1951)