And there's really two different ways to think about it.

One, if you want to be optimistic about the European project, is that the EU could actually be stronger without the UK in it.

To understand how, it helps to look at the history of the EU.

And the idea is to take this continent that is the cradle of a wonderful civilization, but has also been the scene of some incredibly destructive wars, some horrific political crimes, and make sure that kind of thing can never happen again.

And the idea was if they unified the steel and coal industries across national boundaries, they wouldn't be able to fight wars with one another.

But the UK was never completely on board.

They weren't one of the six original countries to join up, they joined a little bit reluctantly, they didn't want to join the single currency project.

And English people have, in a geographic sense, often not felt that they are even quote unquote part of Europe.

So, to an extent, they've always been the marginal member, and if anyone is going to leave, it would be them.

Once the UK is out, the remaining countries might be able to get some important things done, like crafting a common immigration and foreign policy, which the EU doesn't have, and trying to figure out a way to make the common currency work better.

They don't have a common tax policy; they don't have a common welfare state.

It may be easier for the countries that remain to build stronger institutions, and you may ultimately see a stronger, even though it's a smaller, Europe.

That's the optimistic view.

Another view could be that we're looking at the beginning of the unraveling of the whole thing.

You start pulling a thread on the sweater, and it's all going to collapse.

You see polls from France and even Germany, the countries at the very heart of Europe, showing that it's become unpopular.

They don't feel ownership over European politics.

It's a bunch of guys sitting around in a Belgian city, negotiating deals in a language they don't speak.

They don't have a spirit of European patriotism and a deep emotional European identity.

So, the EU has a lot of the attributes of a nation state.

It has a flag, they have a national anthem, but it doesn't have any words.

If you fielded a single EU soccer team, it would win the World Cup every time, but nobody would cheer for it.

So, a lot of how this turns out in the end is going to do with what kind of deal the UK can reach with the EU.

If the UK manages to get out but to then still have a really favorable free trade deal with the EU and really sort of prosper, that's going to make it easier for other countries to say well, they want out too every time a decision happens that they don't like.

So, there's a strong incentive to make this messy, and to make it really as painful as possible.

If EU leaders manage to exact a high price from the UK in leaving, that means that probably the rest of the union is not going to break up.