We argue that several empirical constraints strongly restrict parameters of
the effective microscopic spin model describing $\alpha$-RuCl$_3$. In
particular, such constraints dictate a substantial \emph{positive} off-diagonal
anisotropic coupling, $\Gamma^\prime\!>\!0$, not anticipated previously. The
renormalization by quantum fluctuations allows to reconcile larger values of
the advocated bare parameters with their earlier assessments and provides a
consistent description of the field evolution of spin excitations in the
paramagnetic phase. We assert that large anisotropic terms inevitably result in
strong anharmonic coupling of magnons, necessarily leading to broad features in
their spectra due to decays, in accord with the observations in
$\alpha$-RuCl$_3$. Using duality transformations, we explain the origin of the
pseudo-Goldstone mode that is ubiquitous to the studied parameter space and is
present in $\alpha$-RuCl$_3$. Our analysis offers a description of
$\alpha$-RuCl$_3$ as an easy-plane ferromagnet with antiferromagnetic
further-neighbor and strong off-diagonal couplings, which is in a fluctuating
zigzag ground state proximate to an incommensurate phase that is continuously
connected to a ferromagnetic one.