Macbeth, like many of
Shakespeare's plays, is based on true events.
There
really was a King Macbeth of
Scotland, he reigned between 1040 and 1057
AD.
Although he
wasn't ever
thane of either Glamis or Cawdor, he really
was a great
warrior who had to avenge his father's murder. The details are very different, but the seed of the story was there.
On the subject of "the curse" of Macbeth, the play's name is said to have been cursed by 17th Century Witches, who resented real spells appearing in the play's text. For example, in act 4, scene 1
"Round about the cauldron go;
In the poisn'd entrails throw.
Toad, that under cold stone
Days and nights has thirty-one
Swelter'd venum sleeping got.
Boil thou first i' the charmed pot"
Since its opening night in 1604, Macbeth has been notorious for both backstage and onstage accidents and deaths. One such event occurred in 1672, when Macbeth switched the fake dagger with a very real and pointy one, and subsequently killed
Duncan on-stage.