Gramophone Dreams #81: Feliks Envy headphone amplifier
Girard explains how this not knowing drives history and invention. His main premise is that we feel desire but, not knowing what we desire, mimic the desires of others. These "others" we mimic constitute a third element, interrupting the lines of force between a person and the objects desired. This, according to Girard, makes desire, and by extension human evolution, a nebulous but powerful anthropological force engaged in forming human cultures.
In other words, you might like big speakers and fat speaker cables, but maybe only because people around you appear to like them. Same with cars and clothes and lovers.