Let’s say you were an ordinary person living in Greece and had a stash of euros deposited in your local bank. You’ve been watching all the political chaos unfold on TV and listening to chatter about how Greece might have to exit the euro altogether. What would you do?

Get it while you can. (Yannis Behrakis/Reuters)

And that’s exactly what a lot of Greeks have been doing these past two years, withdrawing about €2 to €3 billion worth of euros from the country each month. Lately, though, these withdrawals have been accelerating. A lot. On Monday, Greek depositors took out some €700 million in a single day, sending their euros elsewhere for safekeeping. It’s a smart move by those individuals. The problem, though, is that if everyone in Greece does this, it could inadvertently get Greece kicked out of the euro.

After all, someone needs to replace the lost euros in those Greek banks. Otherwise the banks can’t keep functioning. Recently, Greece’s central bank has stepped in and provided banks with emergency loans — some €60 billion all told. But there are limits to how much aid the central bank can offer (the rules, explained here , have to do with collateral). In theory, the Bank of Greece could get permission from the European Central Bank to inject even more euros into the banking system. But at some point the ECB may just decide it’s not worth pouring endless cash into rickety banks in an unstable country.

In the meantime, the Greek government can’t get its hands on enough euros, either. Many of its attempts to raise revenue are failing. For instance, as the Financial Times’ Masa Serdarevic reports, the government recently tried to force people to pay property taxes by folding them in with electricity bills. In response, Greeks simply stopped paying their electricity bills.

So at a certain point, the Greek banks and government could face a situation in which they no longer have enough euros for their day-to-day operations. ATMs could no longer dispense euro notes. Civil servants and pensions would have to be paid in IOUs. Intense pressure would grow on the government to introduce a brand-new currency — to bring back the drachma, say.

At that point, the country would have no choice but to leave the euro. “Exit, in other words, becomes a fait accompli,” writes Ryan Avent. “The debate over whether or not Greece ought to leave then becomes moot.”

Now, Greece hasn’t reached this stage quite yet. For one, most Greek people (for whatever reason) aren’t taking all of their euros out of Greek banks — about 75 percent of deposits still remain, or about €160 billion. It’s more of a “bank jog” than a bank run. And it’s still an open question whether the European Central Bank will pull the plug on Greece or whether European technocrats will, instead, do everything they can to hold the euro zone together.

But that’s how a bank panic in Greece could become self-sustaining. As Paul Mason puts it, the fate of the euro may now rest in the hands of Greece’s bank customers.

Related: FAQ: What’s wrong with Greece? And can it be fixed?