While many today would say that any misfortune surrounding a production is mere coincidence, actors and other theatre people often consider it bad luck to mention Macbeth by name while inside a theatre, and sometimes refer to it indirectly, for example as "the Scottish play", or "MacBee", or when referring to the character and not the play, "Mr. and Mrs. M", or "The Scottish King".
This is because Shakespeare (or the play's revisers) are said to have used the spells of real witches in his text, purportedly angering the witches and causing them to curse the play. Thus, to say the name of the play inside a theatre is believed to doom the production to failure, and perhaps cause physical injury or death to cast members. There are stories of accidents, misfortunes and even deaths taking place during runs of Macbeth.
According to the actor Sir Donald Sinden, in his Sky Arts TV series Great West End Theatres,
contrary to popular myth, Shakespeare's tragedy Macbeth is not the unluckiest play as superstition likes to portray it. Exactly the opposite! The origin of the unfortunate moniker dates back to repertory theatre days when each town and village had at least one theatre to entertain the public. If a play was not doing well, it would invariably get 'pulled' and replaced with a sure-fire audience pleaser – Macbeth guaranteed full-houses. So when the weekly theatre newspaper, The Stage was published, listing what was on in each theatre in the country, it was instantly noticed what shows had NOT worked the previous week, as they had been replaced by a definite crowd-pleaser. More actors have died during performances of Hamlet than in the "Scottish play" as the profession still calls it. It is forbidden to quote from it backstage as this could cause the current play to collapse and have to be replaced, causing possible unemployment.
One particular incident that lent itself to the superstition was the Astor Place Riot. The cause of the riots was based on a conflict over two performances of Macbeth, and is usually ascribed to the curse.
Several methods exist to dispel the curse, depending on the actor. One, attributed to Michael York, is to immediately leave the building the stage is in with the person who uttered the name, walk around it three times, spit over their left shoulders, say an obscenity then wait to be invited back into the building. A related practice is to spin around three times as fast as possible on the spot, sometimes accompanied by spitting over their shoulder, and uttering an obscenity. Another popular "ritual" is to leave the room, knock three times, be invited in, and then quote a line from Hamlet. Yet another is to recite lines from The Merchant of Venice, thought to be a lucky play. Other sources cite A Midsummer Night's Dream as being a similarly lucky play.