This has nothing to do with Feynman. The deep mystery is always why does nature work the way it does. The QM phase answer provides a deep explanation for why least action occurs at a classical level. I am not sure what your educational background is but QM and Classical are far from equivalent. QM looks like classical under many macro situations.
The quote you wrote exclusively referenced a Feynman book (I suggest you to check your sources), so it was you who brought up Feynman.
> The QM phase answer provides a deep explanation for why least action occurs at a classical level.
No, it does not. The phase in a QM state provides the intereference of the probabilities, which is an integral part in the calculations on the many-paths formulation of QM, it has NOTHING to do in the classical sense.If that is true, please derive the GR action from QM, if you do so a Nobel prize and a seat along Newton and Einstein are waiting for you.
> QM and Classical are far from equivalent. QM looks like classical under many macro situations.
These two statements are contradictory.Maybe you are misremembering the Ehrenfest theorem. If that is the case you are confusing the expectation value of a physical quantity in QM with an actual physical measurement.
