Many years ago Yoga was defined as "the complete mastery of the mind and emotions." You can readily see how great a part concentration plays in reaching this mastery. For as man thinks, so he is. Thus, although we are always being told that it is impossible to change human nature, you, the individual, can indeed change yourself to a very great extent by determining what your thoughts will be. For the mind is wonderfully flexible and will respond to cultivation as fertile soil responds to it. Think peace, and gradually your entire outlook becomes one of serenity and inner calm. Empty your mind of anger, of resentment against your fellow-beings, substitute an attitude of live-and-let-live, and you will be rewarded by a sense of tolerance that will make living with others infinitely easier. Refuse to be ruffled by the thousand-and-one phenomena that yesterday distracted you from your chosen course, and a deep and genuine feeling of equanimity will soon make it easier for you to live with yourself and, of course, with others.
The Yogis go much further. They claim that the mind of each of us influences the minds of others by means of currents we set up. Therefore, they say, harsh and hostile thoughts spread harm and may actually do harm to those who come in contact with us while on the contrary calm and kindness contribute to their well-being. Be that as it may, we do know--and both medical men and psychologists are the first to agree with this--a hostile, negative attitude is invariably destructive both to ourselves and to our relationships with others. The only constructive approach is the positive one. Through practice of Yoga it is possible to achieve such an attitude without having recourse to such long, arduous processes of emotional re-education as people are given on the psychiatrist's couch. It would be the height of folly not to profit by what is at hand.
For the ordinary person, there is, of course, no such thing as complete detachment. The highly- trained Yoga on the other hand is able so completely to detach himself from the world around him that he achieves startling results. For instance, it is basically through intense concentration-- through his single-minded refusal to permit any outside manifestation whatsoever to disrupt it-- that the Indian fakir learns so completely to control his body as to perform the feats for which fakirs are famous. Suspending breath for days at a time, halting the beating of the heart, sitting on a bed of nails without any seeming ill-effects--all these are the more spectacular results of complete, intensive concentration combined with the exercise of highly-developed will power. We in the West aren't interested in such accomplishments. If the fakirs' feats are mentioned here at all, it is only to demonstrate to what extraordinary lengths it is possible to triumph over normal human limitations. Our immediate interest is to learn to benefit from concentration in practical ways.