Many data are needed to "teach" a machine-learning model the rules of chemistry. This is often a problem in chemical kinetics, since we usually have only small experimental datasets, and often the data available is very "clumpy", with many data for certain types of molecule or reactions, and zero data on some other types of molecules or reactions. The need for data is illustrated for solvation free energy in Fig. (orange curve) using calculations and data reported by Vermeire and Green. Molecule 1 Molecule 2