Let's suppose the Greek really spent others money, then, how to prevent other people from spending your money?
A capture fish and sell them to market, B pick fruits and sell them to market, both of them use exchanged shells to buy other products. But from one day, B just buy everything with a long term loan without pick enough fruits, what will happen?
1. The price of fruits will rise due to reduced supply
2. C will produce fruits due to rising prices
3. Fruit price get back to normal
4. B can not produce fruits any more since now the competition is hard (C took his job)
5. B will live on loan and accumulate huge debt
Both A and C thought the money are created by them (or corresponding to wealth created by them), so they can think that B is spending their money, but the essential part is: B is consuming A and C's products without providing any valuable things in exchange. Although B provide money as exchange, he did not contribute to the amount of consumable wealth
How much B should provide in exchange, is very difficult to judge. It is not decided by B's labor, but mostly decided by A and C's desire (if Greece can provide lots of petroleum, it is no problem at all). So, as long as A and C desire money, B can pay them with money, A and C will feel satisfied
A want others to buy his products as much as possible, but on the other side, he will feel unfair if B just buy his products by printing money, this is essentially a moral question, not an accounting or economy question
So, if A can not do anything about B, the only way to prevent B from spending A's money is: A spend the money he earned immediately and exchange to consumable goods, thus he will make sure no one can have access to his labor. But that is also not very practical, due to none of the consumable goods can be kept for long, and transportation and liquidation for them is also troublesome
Then he will realize that if he would like to hold the value in goods form, he will immediately face lots of risk, so finally maybe he still prefer holding the currency, but he will try all he can to stop B from buying his labor with loaned money
So who is the most clever guy here, B of course. He spent big, lived a good life, and have lost his job, thus he has nothing to pay the debt, what the banks can do is only write off his debt and keep going forward. And IMO, since both A and C has earned enough money in this process, they will feel satisfied anyway, why should they blame B? Of course when they start to spend their savings, they will find out that there is not enough goods in the market, but that is many years later, and if that is the case, B will find a job and payback his debt
We need more country like Greece to raise up the GDP for those export based countries