From a book about which David Ogilvy is quoted as saying: "Nobody, at any level, should be allowed to have anything to do with advertising until he has read this book seven times":
"Advertising is salesmanship. Its principles are the principles of salesmanship. Successes and failures in both lines are due to like causes. Thus every advertising question should be answered by the salesman's standards.
Let us emphasize that point. The only purpose of advertising is to make sales. It is profitable or unprofitable according to its actual sales. It is not for general effect. It is not to keep your name before the people. It is not primarily to aid your other salesmen. Treat it as a salesman. Force it to justify itself. Compare it with other salesmen. Figure its cost and result. Accept no excuses which good salesmen do not make. Then you will not go far wrong. The difference is only in degree. Advertising is multiplied salesmanship. It may appeal to thousands while the salesman talks to one. It involves a corresponding cost. Some people spend $10 per word on an average advertisement. Therefore every ad should be a super-salesman.
A salesman's mistake may cost little. An advertisers mistake may cost a thousand times that much. Be more cautious, more exacting, therefore. A mediocre salesman may affect a small part of your trade. Mediocre advertising affects all of your trade.
Many think of advertising as ad-writing. Literary qualifications have no more to do with it than oratory has with salesmanship. One must be able to express himself briefly, clearly and convincingly, just as a salesman must. But fine writing is a distinct disadvantage. So is unique literary style. They take attention from the subject. They reveal the hook. Any studies done that attempt to sell, if apparent, creates corresponding resistance.
So with countless questions. Measure them by salesmen's standards, not by amusement standards. Ads are not written to entertain. When they do, those entertainment seekers are little likely to be the people whom you want. That is one of the greatest advertising faults. Ad writers abandon their parts. They forget they are salesmen and try to be performers. Instead of sales, they seek applause.
The reason for most of the non-successes in advertising is trying to sell people what they do not want. But next to that comes lack of true salesmanship. Ads are planned and written with some utterly wrong conception. They are written to please the seller. The interest of the buyer are forgotten. One can never sell goods profitably, in person or in print, when that attitude exists."
Claude C. Hopkins, Scientific Advertising, 1923 (pdf)