Just a quick question. Why do the Continental Europeans on this endlessly tedious thread seem to care so much? At the end of the day the people most affected by this will be the British, it's not going to affect the rest of the EU past importers and exporters. Why care so much?
Like others said, the EU is more than just trade. It goes back to WWII. The foundation of the European project always has been to prevent an armed conflict between its members by closely cooperation. This is most evident in economic cooperation, but it goes much deeper than that. Worker's rights, for instance, a minimum is enforced within the EU. Fair and free trade, anti-corruption, antitrust etc.
Freedom of movement is one of the fundamental pillars of the EU. So as a European citizen, I can live anywhere I like within the EU. No hassle, I can just do it. So personal freedom is extended and now is a bit restricted by the UK leaving. Privacy laws which have been introduced, and are compulsive for even US tech companies. Fair taxes, tax evasion etc. can be introduced because companies can't ignore the 510million consumers within the EU. Rich countries helping first the south and now eastern European countries to develop to raise the overall level of wealth within the EU, solidarity.
Nowadays it goes even further, individual countries within the EU aren't that important in the world, that makes the EU even more relevant today, than ever before. The EU is founded on common ethics and beliefs. Those we take for granted now, but we shouldn't. The rise of the populist movement is evident all over the world. Those populists don't embrace those human rights all that much. Criticism on free media, free and impartial justice system, the democratic value's etc. All those rights are guaranteed by adopting EU directives and treaties.
So those are just a small portion of the reasons why we care so much. We hate for our cousins across the North Sea to miss out on all of that. It, indeed, feels like a close relative which is breaking with the family. It is because we care about the British, we are so involved (and it affects us all within the EU).