There has arisen in our time a most singular fancy: the fancy that when things go very wrong we need a practical man. It would be far truer to say, that when things go very wrong we need an unpractical man. Certainly, at least, we need a theorist. A practical man means a man accustomed to mere daily practice, to the way things commonly work. When things will not work, you must have the thinker, the man who has some doctrine about why they work at all. It is wrong to fiddle while Rome is burning; but it is quite right to study the theory of hydraulics while Rome is burning.
It is then necessary to drop one’s daily agnosticism and attempt rerum cognoscere causas. If your aeroplane has a slight indisposition, a handy man may mend it. But, if it is seriously ill, it is all the more likely that some absent-minded old professor with wild white hair will have to be dragged out of a college or laboratory to analyze the evil. The more complicated the smash, the whiter-haired and more absent-minded will be the theorist who is needed to deal with it; and in some extreme cases, no one but the man (probably insane) who invented your flying-ship could possibly say what was the matter with it.