Halliday & Matthiessen (2014: 226):
… another term that has been used for this function is Patient, meaning one that ‘suffers’ or ‘undergoes’ the process. … the relevant concept is more like that of ‘one to which the process is extended’. The concept of extension is in fact the one that is embodied in the classical terminology of ‘transitive’ [‘going through’] and ‘intransitive’ [‘not going through’], from which the term ‘transitivity’ is derived.