The origins of the "curse of Macbeth" are shrouded in mystery, but the most commonly cited reason for the curse is the belief that Shakespeare used authentic witches' curses in the text, thereby investing it with bad luck. Believers point to a long and semi-apocryphal list of accidents as evidence.
Typically, to ward off the curse, actors are forbidden to speak the name of the play, referring to it only as "Mackers" or "The Scottish play." If someone inadvertently speaks the forbidden name, they must perform a cleansing ritual. This usually involves spinning around three times, spitting, swearing, leaving the theater and being re-admitted, or reciting a specific line from a different Shakespearean play. Particularly superstitious actors may use a number of these charms at once in order to cleanse themselves of the play's evil taint.