ABSTRACT
Because reactive controllers are idempotent they are simple to use, but they also have serious drawbacks. For example, because a reactive controller cannot remember previous percepts and actions, it cannot remember which action it picked last time it was in the same situation. When it finds itself in the same situation as before, it cannot therefore decide to pick a different action from before. If last time the choice turned out to be a bad one, then a reactive controller will carry on making the same mistake over and over again, just like a fly repeatedly hitting a window pane. Since there is no way for it to distinguish seeing a situation once to seeing it a thousand times, it cannot even count how many times it has been in the same situation before.
