D.1. Significance of Role of Perception: Since along with knowledge and control of a thing, the human perception of presence of a need, and of useful properties define an object or an action as having Good Characters, misperceptions are possible, and can play a significant role.
E.1. Menger on more than one occasion informs us of the role of misperception, and thereby signifies the role of perceptions.
E.2. First, he distinguishes two imaginary goods. These are either goods which serve a need which is non-existent but is still perceived to exist or goods which do have any useful properties but still are perceived to have such properties. (See Imaginary Goods).
E.3. Menger reminds of us this role of perception once more, and with emphasis when discussing The Causal Order of Goods. When everything in an advanced economy functions smoothly, as is during times of stability, producers who only produce intermediate goods i.e. goods which themselves have are not for consumption but required for production of them, these producers, due to stable supply of other complementary goods (See I in The Primacy of One-To-Many Relations), and consequent stable demand of their good by manufacturers of first order goods begin to perceive as if their goods have the same good characters as first order goods.
Put simply, during good times since everyone produces without interruption, each producer of complementary intermediate goods suffers a misperception that his or her good has good characters i.e. has its own demand independent of complementary goods. This misperception ends when stable times are disturbed by a sudden change, and at least one of the suppliers of complementary goods fails to supply, and as a result, the demand of other complementary goods by producers of final goods also fall.
E.4. Accordingly, all of these establish the significance of perception. However, I believe as apprentices of Economics, it is our task to understand the sources of misperception and then correct our perception and in so doing establish a rational order of things i.e. avoid misperception and uphold rationality where it has been suppressed.
Reference: Menger, Carl (2004). Principles of Economics, Online edition, The Mises Institute, 2004. (Chapter 01 pages 53-54 and 62-63)