  In this paper, we present a theoretical framework for understanding the
Extremely Correlated Fermi Liquid (ECFL) phenomenon within the $U=\infty$
Hubbard model. Our approach involves deriving equations of motion for the
single-particle Green's function $G$ and its associated self-energy $\Sigma$,
which involves the product of the bosonic correlation function comprising both
density ($D_N$) and spin ($D_S$) correlations with $G$. By solving these
equations self-consistently, we explore the behavior of $G$, $D_N$, and $D_S$
as functions of frequency, temperature, and hole concentration. Our results
reveal distinct coherent and incoherent Fermi liquid regimes characterized by
the presence or absence of quasiparticle excitations. Additionally, we analyze
the intrinsic dc resistivity $\rho(T)$, observing a crossover from $T^2$ to
linear behavior with increasing temperature. Our findings delineate Fermi
liquid, quantum incoherent, and `classical' regimes in strongly correlated
systems, emphasizing the importance of quantum diffusive local charge and spin
fluctuations.
