The tidal-wave theory is inspired by the particular morphology of the cerebellar cortex. It elegantly attributes function to the anisotropy of the cerebellar wiring and the geometry of Purkinje cell dendrites. In this commentary, physiological considerations are used to elaborate temporal and spatial constraints of the tidal-wave theory. It is shown, first, that limitations of temporal precision in the cortical inputs to the mammalian cerebellum delimit the spatial resolution of an input sequence (i.e., the minimal distance along the parallel fibers which can detect sequential input) to the range of a millimeter at best. Second, temporal characteristics of Purkinje cell postsynaptic potentials are argued to predict a distance of at least several millimeters along the parallel fiber beam in order to generate a sequence in the cerebellar output. It is concluded that the implementation of tidal waves as a general principle of cerebellar function is questionable as there exist cerebelli too small to match these constraints.