``This enormous difference,'' Mr. Taylor goes on to say, ``exists in all the trades and branches of labor investigated, from pick- and-shovel men all the way up the scale to machinists and other skilled workmen. The multiplied output was not the product of a spurt or a period of overexertion; it was simply what a good man could keep up for a long term of years without injury to his health, become happier, and thrive under.'' Ask the head of any important business what is the first qualification of a foreman <p 6> or manager, and he will tell you ``ability to handle men.'' _Men who know how to get maximum results out of machines are common; the power to get the maximum of work out of subordinates or out of yourself is a much rarer possession_. Yet this power is not necessarily a sixth sense or a fixed attribute of personality. It is based on knowledge of the workings of the other man's mind, either intuitive or acquired. It is the purpose of this and succeeding chapters to consider some of the aspects of human nature that can be turned to advantage in the cultivation of individual efficiency and the elimination of lost motion and wasted effort. In a thousand instances, in factory and market place, unrecognized use has been made of the principles of psychology by business men to influence other men and to attain their ends. _For the science of psychology is in respect to certain data merely common sense, the wisdom of experience, analyzed, formulated, and codified_. <p 7> _It has taken its place, alongside physics and chemistry, as the ally and employee of trade and industry_. The time has come when a man's knowledge of his business, if the larger success is to be won, must embrace an understanding of the laws which govern the thinking and acting of the men who make and sell his products as well as those others who buy and consume them. The achievements of the human mind and the human body seem to many to be out of the range of possible improvement through application of any science which deals with these human activities. Muscular strength and mental efficiency seem to be fixed quantities not subject to increase or improvement. _The contention here supported, however, is that human efficiency is a variable quantity which increases and decreases according to law. By the application of known physical laws the telephone and the telegraph have supplanted the messenger boy. By the laws of psychology applied to business equally astounding improvements are being and will be secured_. <p 8> Employers sometimes find that their men are not working well, that they loaf and kill time on every possible occasion. The men are not trying and are indifferent to results. Under such circumstances a new foreman, the dismissal of the poorer workmen, modification of the wage scale or method of payment, or some other device may correct the evil and induce the men to exert themselves.