It took Otmar Issing a mere 5 years to understand that the Euro is a flawed idea.

Otmar Issing, one of the fathers of the Euro, in March 2011:

Issing: ..... A country that behaves correctly pays low interest rates, while one that lives beyond its means pays higher interest.

Which is tantamount to saying, I am German and have no problem with Germany's export surplus based on low wages and low consumption and which puts importing countries into debt, for which my country reaps the benefit of ultra low interest payments on Bunds.

SPIEGEL: Do you expect that Portugal and Spain will have to resort to the bailout fund?

Issing: I would rule it out for Spain. The country is finally on the road to reform. For example, it is cleaning up rigidity in the labor market stemming from the days of the Franco dictatorship. Portugal still stands a chance of making do without assistance.

SPIEGEL: Even should its debt be restructured, Greece would still struggle for years to pay off its loans. Wouldn't it be better to simply exclude the country from the monetary union?

Issing: Such debates are superfluous because they ignore reality. You need to amend agreements to eject a country. This can only be done unanimously. No "candidate" would agree to it. It's a complete waste of time to even think about it.

.....

SPIEGEL: What does this mean for the euro?

Issing: It certainly doesn't mean that it will be dissolved. It's a good bet that the euro will continue to exist for a long time to come. The question is not whether the euro will survive, but which euro will survive. If everyone is liable for everyone else, even in the case of bad policies, it will become more and more difficult for the European Central Bank to defend the stability of the euro.

Fast forward to October 2016.

Otmar Issing on why the euro ‘house of cards’ is set to collapse

Mr. Issing starts off with a missive against Merkel and Schäuble.

Prof Issing said the euro has been betrayed by politics, lamenting that the experiment went wrong from the beginning and has since degenerated into a fiscal free-for-all that once again masks the festering pathologies.
“Realistically, it will be a case of muddling through, struggling from one crisis to the next. It is difficult to forecast how long this will continue for, but it cannot go on endlessly,"

Prof Issing lambasted the European Commission as a creature of political forces that has given up trying to enforce the rules in any meaningful way. "The moral hazard is overwhelming," he said.  
"The ECB is now buying corporate bonds that are close to junk, and the haircuts can barely deal with a one-notch credit downgrade"

"The Stability and Growth Pact has more or less failed. Market discipline is done away with by ECB interventions. So there is no fiscal control mechanism from markets or politics. This has all the elements to bring disaster for monetary union.

"The no bailout clause is violated every day," he said, dismissing the European Court's approval for bailout measures as simple-minded and ideological.

"The decline in the quality of eligible collateral is a grave problem. The ECB is now buying corporate bonds that are close to junk, and the haircuts can barely deal with a one-notch credit downgrade. The reputational risk of such actions by a central bank would have been unthinkable in the past," he said.

"The Greeks should have been offered generous support, but only after it had restored exchange rate viability by returning to the drachma."

There is more here, but overall it all sounds a little self-serving because Prof Issing and others from the Bundesbank were chiefly responsible for this design flaw.