The implausible in pursuit of the indefensible?
When Ireland explicitly guaranteed all the liabilities of the Irish banking system just over two years ago, the finance minister, Brian Lenihan, said it was "the cheapest bank bailout in the world."
It is turning out to be very expensive, not just for Ireland but for the whole of the eurozone. The European ministers meeting in Brussels today know that they have also made promises to the markets that they will find hard to keep.
Let me explain. Ever since this crisis began, the response by European policy makers has been centred around a promise that bondholders would be compensated in full for their investments - and a hope that this proposition would never seriously be tested.
Now that promise is being tested, in Ireland, which probably has the greatest mountain of problematic bank debt, relative to its economy, of any eurozone economy.
European investors and taxpayers look at Ireland, and they start to see what that promise to bondholders actually entails, not just for Ireland but for rest of the zone. And what started out as implausible, begins to look downright indefensible.
I've been banging on about the ECB role in the saga for months (see, for example Greek sovereign debt: Exit closed? and Ireland: A problem soon to be shared). Robert Peston provides a very useful reminder of the numbers involved in his two latest posts (How big is Europe's crisis? and Will the ECB pull the plug on Ireland?)
By providing cheap and unlimited liquidity to banks, the ECB has effectively found itself filling the gap between what the European governments had promised to the bond markets, and what they can actually afford.
It has, to put it mildly, not been comfortable with playing this role. And in recent months senior ECB figures have been making their reservations felt, pressing governments to decide exactly how much they were going to support troubled economies like Ireland, and on what terms.
This has combined with the German chancellor's understandable - but deeply inconvenient - desire to send a message to German taxpayers and the markets that the promise to always and everywhere bail out bondholders has a use-by date. Come 2013, anyone buying eurozone sovereign debt should expect to pay the price for their mistakes (see my post From 'competitive depreciation' to 'competitive miscommunication').
As a result, this looks very like crunch time for eurozone ministers.
As I said on the Today programme this morning, perhaps the biggest flaw at the heart of the eurozone system was its version of the "Three No's": there would no exit, no bail-outs, and no default. That's possible in a perfect world where no country ever gets into trouble.
In the real world, when countries have crises, at least one of these rules will inevitably be broken. The founders planned for success, and didn't make much provision for failure.
In those fateful weeks of April and May, the eurozone governments decided to suspend the ban on bailouts right now, with a quiet promise (to Germany and others) that the "no default" rule would be lifted in future, when the crisis was past. But even here, they were planning for success without really preparing for failure.
Looking at the sovereign borrowing of all of the peripheral economies, and the debts of their banking systems, no serious investor expects every penny of that money to be repaid.
Even if it were possible politically, I doubt there are many people who think it would be healthy for Europe's economy or its democracy to transfer all of those obligations to the public balance sheet, to be financed by repeated rounds of fiscal austerity.
In reality, as we see in Ireland, transferring all of those obligations tends to make a much more damaging sovereign default that much more likely.
Understandably, European governments are desperate to avoid a conversation about how - and how far - the debts of European banks or countries might be restructured. So they keep promising that governments will stand by their banks, and the eurozone system will stand by their governments.
But investors ought to be asking themselves which would be more damaging to the long-term value of eurozone assets: governments breaking their promises to eurozone private bondholders, or governments trying to keep them?
PS You can hear me discussing the consequences of Ireland's economic woes on the rest of Europe with the BBC's political editor Nick Robinson on the Today programme: