Birks – Theories as analogies
Theories are analogies of the real world. They are not the same as the real world. We should not automatically assume that a theoretical finding applies in reality.
Look at this picture: 
It is a photo of an art work, Analogy IV, taken when on display at MALBA (Museo de Arte Latinoamericano de Buenos Aires). It is by Victor Grippo (JunÃn, Argentina, 1936 – Buenos Aires, Argentina, 2002) and dated 1972. It is described as:
“Wooden table, three natural potatoes on pottery plate, metal fork and knife on white linen cloth, three transparent acrylic potatoes on a plate, transparent acrylic knife and fork, on a velvet cloth.”
The right hand side is a representation of the left hand side, but the two sides are not identical. This is clear from the picture despite their similarity to each other. Economic models do not even have a physical similarity to the phenomena they are intended to represent, yet they are often described as if there is nothing to distinguish between them. At best, we could consider them as analogies for the real world. Even then, there are additional reserves, qualifications and adjustments required when relating one to the other.
Commentary added, 6th November 2014