The UK is the first bona fide country to leave. The closest thing prior to this is when Greenland, which is part of Denmark, left in 1985. (The rest of Denmark stayed.) Greece has thought seriously about it though. That would be Grexit (another story altogether). But think about the precedent it sets. With the UK's decision to leave, other EU countries might start eyeing the door too and that'll have huge consequences for the economy and stability. Jan Techau, director of foreign policy think tank Carnegie Europe, said the EU is sure to play hardball when it comes to negotiating the UK's exit.