This truth applies all the more to countries sharing a common currency such as the member states of the euro area. Back in 1999, eleven European countries adopted the euro as their common currency. Today, the single currency is shared by 19 countries and more than 300 million people, which in my eyes makes it a success story.
That said, it has not always been plain sailing. In the wake of the global financial crisis of 2008, the euro area slid into a financial crisis of its own. This was compounded in 2010 when Greece entered into a sovereign debt crisis, triggering a sudden loss of confidence in other member states which eventually brought the euro area to the brink of collapse.