The people of Scotland narrowly voted against independence in September 2014 on the basis of specific promises that Scotland would remain in the EU, and that the Scottish Parliament would become more powerful.  Instead, Scotland is being dragged out of the EU against its will, and powers that the Scottish Parliament has held since its inauguration in 1999 are being taken away.  Either one of those two material changes in circumstances would make the case for a second referendum unanswerable.  The two in combination make it a slam-dunk. 
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