An automobile is constructed to be operated at considerable distances from home; and a man whose knowledge and skill were limited to steering, stopping, starting, and backing the car--who had no knowledge of its details of construction and could not repair a trifling injury--would have very little value as a chauffeur.
A like remark might truthfully be made about the operation of any complex machine; and the more complex the machine, the more aptly the remark would apply.

The chief engineer of any electric plant, of any municipal water-works, of any railroad, of any steamship must have the most profound and intimate knowledge of the details of construction and the method of operation of the machine committed to his charge.

Recognition of this fact by the engineering profession is so complete and perfect as to be almost unconscious; and no man whose reasoning faculties had been trained by the exact methods of engineering could forget it for a moment.

The whole structure of that noble science rests on facts that have been demonstrated to be facts, and the art rests on actions springing from those facts; and neither the science nor the art would now exist, if machines created by engineering skill had been committed to the charge of men unskilled.
It is obvious that the more complicated in construction any machine is, the more time and study are needed to understand it fully; and that the more complicated its method of operation is, the more practice is needed in order to attain skill in operating it.
The more simple the method of operation, the more closely a machine approaches automatism; but even automatic machines are automatic only in so far as their internal mechanisms are concerned; and the fact of their being automatic does not eliminate the necessity for skill in using them.

An automatic gun, for instance, no matter how perfectly automatically it discharges bullets, may be fired at an advancing enemy skilfully or unskilfully, effectively or ineffectively.
In operating some machines, such as a soldier's rifle, or a billiard cue, the number of mental, nervous, and muscular operations is apparently very few; yet every physician knows that the number is very great indeed, and the operations extremely complex--complex beyond the knowledge of the psychologist, physicist, chemist, and biologist.