The Curse of the Nine of Diamonds

It's referred to as "The Curse of Scotland." Is it because the ever-frugal Scots only placed nine diamonds in the Scottish crown rather than the usual ten? Does it refer to a game called, "Pope Joan"? Or because during the 16th-century reign of Queen Mary nine diamonds were stolen from the crown of Scotland by an Edinburgh freebooter called George Campbell? I won't tell you, but you can read all about it here.