Mike uses the analogy of launching a rocket to explain RPE. You have a path, a general idea of what it's going to take to get where you're going, but there will be small course corrections along the way (say due to wind or whatever, I don't know).
You design a training plan for a full cycle. RPE just provides the course corrections along the way by getting the right weight on the bar each day to achieve the desired training effect. TRAC (short daily questionnaire) tells you whether your stress levels are too high, too low or just right and, if necessary, adds or subtracts volume from the plan.