  Observational and theoretical evidence suggests that a substantial population
of molecular clouds (MCs) appear to be unbound, dominated by turbulent motions.
However, these estimations are made typically via the so-called viral parameter
$\alpha_{\rm vir}^{\rm class}$, which is an observational proxy to the virial
ratio between the kinetic and the gravitational energy. This parameter
intrinsically assumes that MCs are isolated, spherical, and with constant
density. However, MCs are embedded in their parent galaxy and thus are subject
to compressive and disruptive tidal forces from their galaxy, exhibit irregular
shapes, and show substantial substructure. We, therefore, compare the typical
estimations of $\alpha_{\rm vir}^{\rm class}$ to a more precise definition of
the virial parameter, $\alpha_{\rm vir}^{\rm full}$, which accounts not only
for the self-gravity (as $\alpha_{\rm vir}^{\rm class}$), but also for the
tidal stresses, and thus, it can take negative (self-gravity) and positive
(tides) values. While we recover the classical result that most of the clouds
appear to be unbound, having $\alpha_{\rm vir}^{\rm class} > 2$, we show that,
with the more detailed definition considering the full gravitational energy,
(i) 50\%\ of the total population is gravitationally bound, however, (ii)
another 20\%\ is gravitationally dominated, but with tides tearing them apart;
(iii) the source of those tides does not come from the galactic structure
(bulge, halo, spiral arms), but from the molecular cloud complexes in which
clouds reside, and probably (iv) from massive young stellar complexes, if they
were present. (v) Finally, our results also suggest that, interstellar
turbulence can have, at least partially, a gravitational origin.
