  Heinz-Dieter Zeh's discovery that the motion of macroscopic objects can not,
under typical conditions, follow the Schr\"odinger equation necessitates a
suitably modified dynamics. This unfolded a long-lasting puzzle in the open
quantum system context: what is the quantum counterpart of the classical
Brownian motion in a gas. Presented is a criticism and an open-end discussion
of the quantum linear Boltzmann and quantum Fokker-Planck equations -- with
constant respect for foundational research.
