Macbeth. Superstitions.

…

…but not entirely true. i.e They told him that he would be king but not how he would become king. The witches told Macbeth who, what, why, where but they did not tell him how and when. So as you can see superstitions were greatly believed and related to in Elizabethan time and the same superstitions were used in the play with a bit of imagination a great play writer and book was written.