  Deciphering the origin of collective phenomena in small colliding systems is
one of contemporary focuses in heavy-ion physics. It entails penetrating the
barrier between two previously separated research topics:
thermalization/hydrodynamization and phenomenological studies of collectivity.
I first review some recent progress in understanding
thermalization/hydrodynamization in large colliding systems, centralized on
bottom-up thermalization. Then, using a simple kinetic theory I demonstrate how
the investigation of hydrodynamization is intertwined with the study of flow in
small colliding systems. Connections of these studies to "hard probes" are also
commented where possible.
