If you are the master of a great factory, and all the machines work by your will, are you happy, restful and peaceful when you come home? You may be the master of a whole army, or of a whole nation, or of many nations - when you are at home, are you peaceful and happy? The answer is "no", and this shows us that another mastery is needed. A man may be the master of a whole army, but if he has a stroke of paralysis all his mastership is gone and he can do nothing. It shows us that this mastership is passing. Mastery of the self is needed. It is not more difficult to gain than the other mastership, but a man will never give as much will-power and spend as many years to master the self, as he does to master a factory, because the results are much less tangible. A factory means: so many pounds tomorrow. The results of the other mastery are much subtler, much less perceptible.