“In reality I am, just like you, convinced that one should look for a substructure, the necessity of which has been cleverly disguised by the current quantum theory through its use of the statistical mold.
I have however long been convinced that one shall not be able to find this substructure in a constructive way from the known empirical relations between physical things, because the required mental leap would exceed human powers. I have arrived at this opinion not only because of the fruitlessness of the efforts of many years, but rather also through the experiences with the gravitation theory. The gravitational equations could only be found by a purely formal principle (general covariance), that is, by trusting in the largest imaginable logical simplicity of the natural laws. As it was obvious that the theory of gravity constitutes only a first step in finding the simplest possible general field laws, it seemed to me that this logical route should first be thought through to the end before one can hope to arrive also at a solution of the quantum problem”