They are usually the link between the director and the rest of the company, and are responsible for the director's visions being passed down to each actor and member of the running crew. They are also responsible for safety and running an orderly backstage area. They maintain the prompt book and the call board, to which rehearsal schedule notes are affixed for the cast. Stagecraft overall has to address the various shortcomings of the stage's spatial and physical limitations. For example, the stage alone cannot be expected to provide wide and distant vistas, or vast spaces where armies gather or huge masses of people congregate. Natural phenomena such as thunderstorms or winds, that are often part of the drama, cannot be recreated in their original form. Furthermore, because of the distance involved, it is difficult for actors to portray the feelings, tensions and passions of their characters to the audience with much distinctiveness. It is for these reasons that special technologies and techniques have been developed from classical times onward to supplement and augment the effects that are to be realised. Technical specialists help to implement these techniques by providing expertise in various areas of the production. The stage manager and their team must ultimately draw all these separate techniques together to create an effective and successful stage production. The "Classical unities" of time, action and place were the main principles of French neo-classical drama during part of the 17th century.They were introduced by Jean Mairet after a misreading of Aristotle's "Poetics", and the critic Castelvetro insisted that playwrights and directors adhere to the unities. In the "Poetics" Aristotle had merely recommended that action should consist only of the main plot without any subplots, and that the time represented by action should not stretch beyond the length of one day. Time merely entered into his recommendations as a hint as to the limits of the attention span the audience could be expected to have. The unity of place, that of the confinement of the action in a play to one locality only, was not mentioned at all.The effect of the three unities on French drama during this period was that their presentation became very restrictive, and it was only when later dramatists began to avoid mentioning specific times and places that the presentation of plays became more creative again. Some dramatists and dramaturgists try to achieve particular effects that are not normally sought in a theatre presentation. Bertolt Brecht coined the term "defamiliarization effect" (sometimes called "estrangement effect" or "alienation effect"; German "Verfremdungseffekt") for an approach to theater that focused on the central ideas and decisions in the play, and discouraged involving the audience in an illusory world and in the emotions of the characters.