The unique selling proposition (USP) or unique selling point is a marketing concept first proposed as a theory to explain a pattern in successful advertising campaigns of the early 1940s. The USP states that such campaigns made unique propositions to customers that convinced them to switch brands. The term was developed by television advertising pioneer Rosser Reeves of Ted Bates & Company. Theodore Levitt, a professor at Harvard Business School, suggested that, "Differentiation is one of the most important strategic and tactical activities in which companies must constantly engage. The term has been used to describe one's "personal brand"; in the marketplace. Today, the term is used in other fields or just casually to refer to any aspect of an object that differentiates it from similar objects.