After discussing all the postulated origins above, the next question is when to identify and introduce new elements into reactivity models. It is essential to avoid creating terms that are redundant, which would only complicate matters unnecessarily. A practical rule of thumb might be to consider defining new elements when the features cannot be reproduced by taking quantitative, linear combinations of formerly defined elements. I will briefly explain this notion with two following examples. Ionic or covalent bonding are not a dichotomy but are rather two ends of a spectrum. However, in some cases, such as with F-F and Me3Si-Cl, experimental results contradict the models of both ionic and covalent bonding and cannot be rationalized merely as "partially ionic plus partially covalent." This discrepancy led to the proposal of a new type of bonding known as charge-shift bonding. The concept of the charge-shift bond is not without controversy, highlighting once again the necessity of continuously questioning the existing paradigm.