To interest people you must write on subjects of which they know something, or subjects which in some way make an appeal to them. You seldom succeed in interesting them if you write of things quite outside their usual range of thought or ideals or aspirations. To ensure some attention from your audience, it is imperative that this matter of personal outlook be taken into account.
A subject may be of enthralling interest to you, but if it is not in any way likely to interest your readers from a personal standpoint—if it has no connection with their spiritual or material life, if it makes no appeal to them on the score of beauty, if they cannot by any stretch of imagination see themselves in a leading part—then it is risky to make that the subject of an early article or book. When you are well-established, and recognised as a capable writer, you can take your chance with any exotic subject you please; but I do not advise it at the beginning of your career.
This does not mean that out-of-the-way subjects should never be chosen. Obviously life would be deadly monotonous if we were always trotting round the same circle. Novelty is most desirable; monotony is fatal to success. But it must be novelty that is linked in some way with the reader's life.
Let us suppose you are absorbed in the study of a certain new germ—a germ that is responsible for much mortality among tadpoles. Not only have you discovered the existence of this germ but you have taken its name and address, inspected its birth certificate, secured its photograph, insisted on knowing its age and where the family go to school, ascertained its average food ration, noted its climatic preferences, and many other useful facts. All this would be very interesting to persons who are rearing frogs; but as such people are few in number, it would scarcely attract the bulk of the reading public, hence you could not expect a book on the subject to have a large sale; nor would an article be likely to find a resting place in a magazine or newspaper that aimed to attract the general public. The subject would have no interest for the majority of people, because once we have left our unscientific youth behind, tadpoles are generally as remote from our life as the North Pole.
But, suppose you suddenly discover that these same germs are communicated by tadpoles to water-cress, and therefore directly responsible for hay fever or whooping-cough (or something equally conclusive); you will find the general public all attention in an instant, since water-cress and whooping-cough make a personal claim on most of us. And in that case your writings would find a market at once.
A Novel must have "Grit" Somewhere in its Composition
The same ruling applies to fiction. Study any successful novelist, and you will see how his knowledge of the things that appeal to men and women guided him in the choice of a subject, and his manner of presenting it.
Some beginners think a peculiar plot, or a bizarre background, or an eccentric subject is more likely to command attention than familiar topics; but that depends entirely on what there is in it likely to appeal to the reader and rivet his attention. Mere eccentricity or peculiarity will not in itself ensure the reader's permanent interest; behind the externals there must be something with more "grit" in it.
While newness of idea is much to be desired, and a breaking-away from hackneyed scenes and types should be aimed for, there must be a strong underlying link to connect the unusual idea with the reader's sympathies and mental attitude. You may lay the scene of your story in the Stone Age, or make your hero and heroine some never-heard-of-before dwellers in the moon; but unless you can interweave some fundamental human trait, or some soul longing that will make such a story understandable to ordinary humanity, it will not interest average readers, since they know very little about the tastes and manners and customs of the folks who lived in the Stone Age; neither are they likely to be at all convinced, nor particularly excited, because you tell them certain circumstances about beings, said to be in the moon, who could never possibly come their way.
Mere Eccentricity will not hold the Public