  Gravity drives the collapse of molecular clouds through which stars form, yet
the exact role of gravity in cloud collapse remains a complex issue. Studies
point to a picture where star formation occurs in clusters. In a typical,
pc-sized cluster-forming region, the collapse is hierarchical, and the stars
should be born from regions of even smaller sizes ($\approx 0.1\;\rm pc$). The
origin of this spatial arrangement remains under investigation. Based on a
high-quality surface density map towards the Perseus region, we construct a 3D
density structure, compute the gravitational potential, and derive eigenvalues
of the tidal tensor ($\lambda_{\rm min}$, $\lambda_{\rm mid}$, $\lambda_{\rm
max}$, $\lambda_{\rm min} < \lambda_{\rm mid} < \lambda_{\rm max}$), analyze
the behavior of gravity at every location and reveal its multiple roles in
cloud evolution. We find that fragmentation is limited to several isolated,
high-density ``islands''. Surrounding them, is a vast amount of gas ($75 \%$ of
the mass, $95 \%$ of the volume) that stays under the influence of extensive
tides where fragmentation is suppressed. This gas will be transported towards
these regions to fuel star formation. The spatial arrangement of regions under
different tides explains the hierarchical and localized pattern of star
formation inferred from the observations. Tides were first recognized by
Newton, yet this is the first time its dominance in cloud evolution has been
revealed. We expect this link between cloud density structure and role gravity
to be strengthened by future studies, resulting in a clear view of the star
formation process.
