Think of it like an invisible spider web, silently linking together people and places. Or perhaps it's more of an invisible road network, or an invisible electrical grid: a system that facilitates transactions, that makes it possible to board an airplane in one country and arrive in another, to trade spare parts across borders, to benefit from international insurance agreements and accepted rates of exchange.
In truth, there is no metaphor that fully encapsulates the rules, laws, arbitration procedures, mutually respected standards and other agreements that make up the international trading system in the 21st century. It is a thing unto itself.
In the past, long-distance exchanges of goods and people usually took place within empires - the Roman Empire, the British Empire - or else depended on the implicit threat of force: If you don't fulfil your contract, we'll bomb your port or beat up your emissary.
In places that don't have a legal framework for commerce and trade, that's how things still work.
In the early 1990s, I met a young "businessman" in Ukraine who explained to me that he only did deals with cousins. His family members, fanned out across several cities, swapped and bartered with one another because they trusted no one else. He was operating in a lawless space - a world most of us can't remember.
More than that: Most of us have grown so accustomed to the opposite, to a world of mutually agreed upon and peacefully enforced global laws, that we no longer appreciate it. Many of us have begun to dismiss the rules as "bureaucracy", those who write them as "needless experts", the law-based order as a sinister plot.
So what if it all disappeared? This isn't a theoretical question.
Some version of that cataclysm might take place in March 2019, if not earlier, in Britain. This weekend the complex set of British-European divorce agreements hit yet another in a long series of predictable snags.
A minority, but a loud minority, in Britain now wants to drop the talks and go cold turkey: carry out a "hard Brexit", a sudden withdrawal from four decades of jointly constructed European Union law, but without any transition deals to fill the gaps.
With apologies to my British friends - and to their children, whose lives would be profoundly affected - I am beginning to think that a really hard, really abrupt Brexit would serve a useful purpose for everybody else.
You don't appreciate the finely regulated, smoothly running, carefully negotiated world we inhabit? Try living outside it.
Among the things that could happen, if nothing is done to prepare: All air travel between Britain and the EU could stop, because if Britain leaves the Open Skies agreement, which it joined as an EU member, airlines will not be able to land there.
Trucks - filled with spare parts or fresh produce - would accumulate in long lines at the ports, since neither British nor European Customs operations are prepared to apply the new tariffs that would appear as the free-trade agreements ceased.
Britain's eight nuclear plants would slowly run out of fuel and parts, since the country would no longer be part of the Euratom regulatory body and cannot purchase nuclear equipment from outside it. British banks, among the world's most international, would abruptly lose the right to serve European customers. Further side effects could include shortages, as trade ground to a halt; inflation, especially in food, as imports dried up; and the loss of health insurance for Europeans living in Britain and Brits living in Europe.
There will be at least 759 treaties to renegotiate, according to the Financial Times. These include dozens of trade agreements with non-European countries, from Canada to Chile, as well as treaties regulating such varied topics as fishing rights and anti-trust law. Each one requires teams of lawyers, meetings, time and negotiation.
Whatever happens, Britain will surely require vast new numbers of bureaucrats, people to work on the new arrangements and people to enforce them.
It will almost certainly turn out that Britain saved money by being part of Europe, because economies of scale made regulation much cheaper.
It will almost certainly turn out that Britain was more powerful - with more sovereignty - when it was part of a large organisation with international clout. Many of the other parties to those 759 deals will seek to take advantage of an isolated country with far fewer allies. British consumers, workers and entrepreneurs will pay the price.
There are plenty of people who don't believe or foresee this scenario. Former Tory minister John Redwood has been tweeting with great confidence about how easy it will be to trade outside Europe. Others have echoed him, and maybe they're right.
But if they aren't - then the sight of Britain's sudden banishment to a world where you are better off dealing with cousins will be a useful tonic for everybody else.