"Out of equilibrium". It is often said in both the context of molecular motors and self-assembled materials that a system is "out of equilibrium"indeed, living systems, which many artificial systems cite as inspiration, are often described as operating "far from equilibrium". The same term is also often applied to describe the molecular motor or self-assembled structures themselves. The latter is problematic because it is not clear what it means for an individual molecule or self-assembled structure to be out of equilibrium in the abstract sense. 43 More correctly, the relative concentrations of molecules can be "out of equilibrium" (i.e., not in accord with the corresponding equilibrium constants) with respect to those of species with which they can potentially exchange, but this is not often specified in such discussions. We also note that any metastable system would meet this definition; NaOAc-based hand warmers are useful, but no one is suggesting that they are cutting edge science.