Just as the Covid-19 vaccines rollout hit the "ramping up" gear we had all been promised,
it could be facing the situation of Slim Dusty's famous pub with no beer.
There were willing arms, loads of vaccinators and a boom in the vaccination centres. The rollout was going swimmingly. Too swimmingly.
Last week, Covid-19 Minister Chris Hipkins said if it kept going that well, there might not be any vaccines.
The danger point will come in the next month, ahead of expected large deliveries from Pfizer in October.
The Government is now faced with the potential embarrassment of putting the vaccines rollout into the fast lane, only to have to force it back into the slow again.
Having urged everybody to get vaccinated, Ardern rather hopefully suggested there was no problem at all with supply – but perhaps there was a problem with the demand side.
In an outbreak, a demand for vaccines is the very opposite of a problem.
The options including jabbing until the vaccines ran out and then pausing or slowing down the rush by limiting booking slots to eke the remaining vaccines out until enough new ones landed.
Both would see the same number of arms jabbed, and the first would see them done more quickly. But the first would also be the most embarrassing for the Government because it would have to pause the rollout altogether.
The third option was getting more vaccines, and getting them now.
That is by far the least embarrassing option for the Government, and despite Ardern's claim there was no problem with supply, it is understood that is exactly what they are now trying to do.
Ardern has said she would set out the Government's plan to deal with the potential problem today or on Tuesday.
The expectation is that the Government has cut a deal with another country to buy or trade vaccines.
It was a step the Australian Government took after moving in New South Wales to try to simply vaccinate its way out of an out-of-control Delta outbreak.
Australia bought one million extra Pfizer doses from Poland earlier this month.
If things get really desperate, there are the agreements for other vaccines as an emergency back up option. But, as the PM has pointed out, our system is currently only set up for Pfizer's requirements.
And having repeatedly told us that Pfizer is the gold-standard – and used that to justify a slower rollout rather than use other types – it will take some sales job to persuade people that another variety is just as good.
It would risk having people delay getting vaccinated until they can be offered Pfizer.
The emergency trade will come at a price. Not least, if it is a trade to take vaccines now in return for New Zealand's vaccines later, it could leave us short if boosters are needed.
It will also still be embarrassing for the Government, which was already criticised by the Opposition for not securing supplies early enough.
But it would at least save the rollout from pausing just as it needed to keep going.
There is more stake on vaccines now than before. Before the vaccines were simply to try to get us to the point we could open the borders.
The end of the year was an okay deadline. But after Delta arrived, that deadline is no longer quite so reasonable. As in other countries before ours, for some that vaccine is life or death.
There is nothing good about a Delta outbreak but, as in other countries, it has jolted people out of any complacency.
The argument it could be put off for another day no longer washed.
It helped that going to get a vaccine is one of the few outings allowed under level 4.
Adding to the rush was the Government's decision to bring forward the start dates for the younger cohorts, as more and more vaccine centres opened up.
People are now pouring in, at a rate of 90,000 a day, all keen to do their bit for the country by getting a jab.
The Government can't afford to fall down in its bit.