  High $T_c$ cuprate superconductors are characterized by two robust features:
their strong electronic correlations and their intrinsic dynamical local
lattice instabilities. Focusing on exclusively that latter, we picture their
parent state in form of a quantum vacuum representing an electronic magma in
which bound diamagnetic spin-singlet pairs pop in and out of existence in a
Fermi sea of itinerant electrons. The mechanism behind that resides in the
structural incompatibility of two stereo-chemical configurations Cu$^{\rm
II}$O$_4$ and Cu$^{\rm III}$O$_4$ which compose the CuO$_2$ planes. It leads to
spontaneously fluctuating Cu - O - Cu valence bonds which establish a local
Feshbach resonance exchange coupling between bound and unbound electron pairs.
The coupling, being the only free parameter in this scenario, the hole doping
of the parent state is monitored by varying the total number of unpaired and
paired electrons, in chemical equilibrium with each other. Upon lowering the
temperature to below a certain $T^*$, bound and unbound electron pairs lock
together in a local quantum superposition, generating transient localized bound
electron pairs and a concomitant opening of a pseudo-gap in the single-particle
density of states. At low temperature, this pseudo-gap state transits via a
first order hole doping induced phase transition into a superconducting state
in which the localized transient bound electron pairs get spatially phase
correlated. The mechanism driving that transition is a phase separation between
two phases having different relative densities of bound and unbound electron
pairs, which is reminiscent of the physics of $^4$He - $^3$He mixtures.
