  At the back of succeeding measurements of anomalies in semileptonic decays at
LHCb and several collider experiments hinting at the possible violation of
lepton flavor universality, we undertake a concise review of theoretical
foundations of the tree- and loop-level $b$-hadron decays, $b \to c l \nu_l$
and $b \to s l^+ l^-$ along with experimental environments. We revisit the
world averages for $R_{D(D^*)}$, $R_{K(K^*)}$, $R_{J/\psi}$, and $R_{\eta_c}$,
for the semileptonic transitions and provide results within the framework of
the relativistic independent quark model in addition to the results from
model-independent studies. If the ongoing evaluation of the data of LHC Run 2
confirms the measurements of Run 1, then the statistical significance of the
effect in each decay channel is likely to reach 5~$\sigma$. A confirmation of
these measurements would soon turn out to be the first remarkable observation
of physics beyond the Standard Model providing a wider outlook on the
understanding of New Physics.
