If you share a country with others, you sign up to sharing burdens and risks. It also means you sign up to sharing successes and riches.
In Europe today some of the separatist movements are from parts of countries that are richer than the rest. They get fed up with sharing their success with others. Thus many in Catalonia in Spain, Padania in Northern Italy and Flanders in Belgium think they would better off without the poorer parts of their countries which they have to help finance.
The case of Scotland is a bit different. Scotland is not the pre-eminent richest part of the UK. London is. However, Scotland feels rich thanks to the presence of oil reserves. Much of the debate about Scottish independence entailed the two sides throwing around different calculations of tax revenues, income per head and general prosperity depending on how much of the oil was regarded as Scotland’s, and how bullish you were about future levels of extraction and future oil prices.
The case of Greece is similar. Germany and other richer parts of the Euro Union do not want to accept full burden and risk sharing with Greece in the way West Germany does with East Germany or Northern Italy does with southern Italy. Germany says No to propping up Greek banks, to sending Greece more money to pay benefit bills or for local authority programmes.
The Scottish case has served as a great reminder of why risk sharing and burden sharing can help. Scotland now has to accept that volumes of oil extracted will be well down on peak levels, and at least for the time being prices well down on Nationalist expectations last autumn. If Scotland were on her own that would mean big spending cuts. Inside the UK the loss of revenue is manageable, and it will be covered from elsewhere.
It reminds us that to be a successful union most in the union have to accept the idea that success is shared and risks are underwritten throughout the whole union. Because many parts of the Euro area are not ready top accept that, the area will remain crisis ridden and unhappy.