Every conversation we've had about the EU for the last five years or so. The entire world has been talking about the relative lack of wisdom of trying to hold the entire EU to one currency for a long time, financial mismanagement, Germany strong-arming Greece into plans not good for them while Greece holds the threat of leaving over the entire EU to get better deals, and all sorts of such financial issues for a long time now. Speculations that the EU was on the path to a breakup have been rampant for years, even
before immigration issues were being discussed. Only now that the breakup might actually be happening is it a total surprise to everyone.
(I'm surprised more people aren't celebrating Brexit. Before Brexit, the EU had all kinds of problems. Now suddenly they've all been solved, apparently. The selfless sacrifice of the UK should be celebrated by the EU, since apparently all the bad stuff is going to happen to the UK, alone. That's the problem with the "turn up the heat" approach to making people do things in politics; it may make people more likely to do things, but not necessarily the things you wanted.)