Quantum Mechanics is the first purely symbolic model associated to external
reality. Such a model is "pure", because it cannot be translated or associated
with any image model. This is a very high step in the evolution of the brain
(level 5 of evolution).
Based on data, it seems that Max Planck understood from the beginning that his
theory was good, but he was blocked by the fact that imagination does not work
in understanding it. It seems that Albert Einstein pushed him to publish the
theory.
Quantum Mechanics cannot be translated to image models. If someone forces such
a translation, aberations or logical contradictions occur. The best known
problem is the nature of light. Quantum Mechanics predicts that light is both
wave and particle. This situation cannot be understood based on image models.
Quantum Mechanics pushed forward the evolution of society on a very high
technological level (e.g. the transistors and the lasers are the basic
components to build computers).