The rate M˙∗ at which matter accretes is therefore regulated by internal torques and radiative processes. Only if M˙∗ = M˙0 = const everywhere, with M˙0 being the outside mass supply, can the accretion process be stationary. Since the internally determined M˙∗ may change due to instabilities, limit cycles, etc., an occurrence of a really long-term steady accretion flow should be considered a fine-tuned eigenstate. Note, too, that in many astrophysical situations M˙0 is also genuinely variable.