An old theatrical superstition has it that saying "Macbeth" inside a theater will cause disaster, so thespians have taken to calling Shakespeare's drama by that name "The Scottish Play."
The Scottish usurper in the production is perhaps the original cause: he toys with witches and their goddess Hecate, and they're all of the sort to lay hexes and predict gloomy fates.
The weird sisters have their own take in the matter -- after all, it's as the title character approaches that one intones:
By the pricking of my thumbs,
Something wicked this way comes.
- Macbeth, Act IV, scene i
Thus, as the witches would have it, the author of the play's regicide is the wicked thing.
Macbeth would have done better to remain small and good as a battlefield hero rather than go for the big and bad ambition that inclined him to reason that failure was worse than murder.
Stage actors who slip and utter the forbidden name can be forgiven by recourse to another superstition, which involves exiting the theater and reciting this line:
Angels and ministers of grace defend us.
- Hamlet, Act I scene iv
It's a worthwhile prayer for all of us.