  Quantum mechanics, one of the most successful theories in the history of
science, was created to account for physical systems not describable by
classical physics. Though it is consistent with all experiments conducted thus
far, many of its core concepts (amplitudes, global phases, etc.) can not be
directly accessed and its interpretation is still the subject of intense
debate, more than 100 years since it was introduced. So, a fundamental question
is why this particular mathematical model is the one that nature chooses, if
indeed it is the correct model. In the past two decades there has been a
renewed effort to determine what physical or informational principles define
quantum mechanics. In this paper, recent attempts at establishing reasonable
physical principles are reviewed and their degree of success is tabulated. An
alternative approach using joint quasi-probability distributions is shown to
provide a common basis of representing most of the proposed principles. It is
argued that having a common representation of the principles can provide
intuition and guidance to relate current principles or advance new principles.
The current state of affairs, along with some alternative views are discussed.
