I don't think that's an actual myth.
It's that Germany never expected or planned to fight such a massive war for as long as they did. Germany's leaders based their decisions on the assumption that they would have a nice short and limited "Silesian war" (Poland in 1939), that an accomodation could be reached with Britain as fellow nordic when Germany did plan a major war in 1942, and that the Soviet Union would collapse in 6 months. Based on their assumptions, Hitler and Germany based their economic decisions in a way to balance the needs for those limited, short term wars, and other considerations (like Hitler's obsession that the Dolchstosslegende meant that German civilians needed to be assured of good times or would turn against him).
This was the general problem with all the Axis countries. Japan never thought the Marco Polo Bridge Incident would mean an 8 year war with China, and it thought the US would agree to a negotiated peace after 6-12 months. Italy thought the war would be over in a few months when Mussolini declared war on France and Britain.
In contrast, all the Allied countries assumed the war would be prolonged and require mass mobilization of society to insure victory. Nationalist China always intended to drag the war out as long as possible. Both Britain and France assumed they would never several years of military build up before they could launch a successful attack on Germany. The US likewise expected a very long war. Only the Soviet Union possibly expected a short war where they were the offensive power, but by 1942 pretty much expected it would take years to end (in contrast, Hitler still thought Soviet reserves were basically gone in late 1942 and that the war in the east would be over soon).
Because of their different conceptions of how long the war would last, each side made vastly different decisions on how to husband their resources.
It was only after Stalingrad that it really sinked into Hitler's mind that he was in for a long, bloody struggle that meant the entire German society needed to be enrolled for "Totaler Krieg" or that he should abandon chimerical wishes that Germany should divert resources to building a surface navy to prepare for a future war with the USA.