Almost a hundred years ago, in 1915, Wilhelm Nusselt published a paper entitled Das Grundgesetz des Warmeuberganges (The Fundamental Law of Heat Transfer), which is often quoted in modern textbooks in this field of engineering science. Most of these modern textbooks, however, still use the notion of three mechanisms, modes, or kinds of heat transfer. Nusselt demonstrated, in this mentioned paper, that convection is nothing but conduction to a moving fluid. Nusselt's paper, however, usually is not quoted for this logical conclusion from facts already known in the late 19th and early 20th centuries, but for the principle of similarity or dimensional analysis, leading to the well-known dimensionless numbers widely used in fluid mechanics and heat transfer. The reasons for the reluctance of most (but fortunately not all) present-day experts to follow Nusselt in his logical argumentation have a number of mainly historical roots. This paper tries to explain why teaching our students that there are two mechanisms of heat transfer has a number of advantages over the classical method that is again and again repeated in our heat transfer literature.