MPE asks the isReady question to the State Variable which in turn asks the Controller. This question is asked before the start of each goal. (Actually, MPE will keep asking this question until isReady returns true, or system deems it impossible to start the goal But all the asking of isReady happens before the start of the goal.) It is asked before the satisfiable question. MPE has to know that the system is ready to start before it can start executing the goal, hence the need to ask isReady.