Both operando characterization and predictive-quality multiscale modeling have by now firmly established that significant structural, compositional and morphological evolution of working catalyst surfaces is more the norm than an exception. Less clear is to which degree the dynamics of this evolution couples to the actual reaction chemistry. The very concept of an active site implies that the corresponding geometric and compositional motif prevails over time scales (much) longer than the catalytic cycle. Translated to the level of the involved elementary processes, this means that the processes underlying the operando evolution of the working surface are rare on the time scale of the molecular processes involved in the catalytic reaction. Identification of the active sites is frequently stated as a central objective for mechanistic understanding and rational catalyst design. Seen from the perspective of operando evolution, making this statement thus equates to (knowingly or unconsciously) assuming such a separation of time scales. The motif of a given active site must persist for long enough, say at least a few catalytic turnovers. Otherwise it makes no sense to characterize and discuss it.