This concept is the brain child of Rosser Reeves who popularised it in the 1950s, and codified it if a 1961 Random House book Reality in Advertising.
Reeves defined USP as a proposition to the consumers which is so strong that it can move the mass of millions, i.e. pull them over to our product. He contends that the consumer tends to remember just one thing from an ad — one strong claim or concept. Each ad must make a proposition to the consumer.
A crucial part of Reeves’ theory is that the proposition or promise made by the ad must be one which the competition has not so far made. It is unique He also expected the marketer to give reasons for the effectiveness of the unique proposition. At its face value, this concept is alright . Technological capability was so unique in his days that others took years to catch up with it. But these days benefits and capabilities no longer remain unique for a long time. In his days, Reeves strategy of product diffentiation was viable, but is no longer valid today. A technological or functional advantage cannot sustain a product/brand for long. We are in an age of parity.
Revees doctrine suggests that consumer behaves rationally. Research and common sense suggest that this is not so.