The phrase that Jacinda Ardern and Ashley Bloomfield have drawn on to justify a three-day lockdown for Auckland after three family members tested positive is "an abundance of caution."
The question is: when is an "abundance" and "over-abundance?" When is there too much caution?
That judgment can only be made in hindsight.
If it turns out from test results this Tuesday and Wednesday that Covid-19 has spread well beyond the mother, father and daughter from South Auckland, and has been silently transmitting through the community, the lockdown decision will be judged to have been justified.
If it turns out to be limited to the family and a small number of contacts, a three-day lockdown for the largest city may in hindsight be judged to have been overkill.
For Jacinda Ardern, the benefits of stopping chains of transmission before they get out of control outweigh the risks of being accused of over-reacting.
The last time Cabinet plunged Auckland into lockdown was back in August and the "Auckland August Cluster" ensued with a total of 179 cases linked to it.
The main debate was not whether or not the lockdown had been justified. With so many cases, there wasn't an argument about that.
The debate was about how long it went on for. It started as a three-day lockdown, like the current one, but eventually lasted much longer, from August 12 until September 1 when Auckland moved to level 2.5 - and the full freedoms of level 2 like mass gatherings weren't introduced until September 23. It joined the rest of the country at level 1 only on October 8.
Yesterday's decision to put Auckland into lockdown was made the same day as the results came through and it initially involved only one family, as happened in August.
There are several differences, however, which may temper support for the current lockdown. The August winter lockdown was after 102 days of no community transmission and there was no known link to the border – in fact one was never established.
This summer lockdown comes at a time when New Zealand was not only relishing its freedoms, but it was feeling confident about its ability to contain Covid-19 in the community because there have been several in the past five weeks. Each of them had a link to the border.
The Prime Minister herself has made much of New Zealand's contact tracing and ability to contain the virus, not least when she expressed displeasure at Australia cancelling flights from New Zealand for five days because of the Northland case.
In the current cases, there is also a likely credible link to the border, through the mother's work in which she handles laundry from planes.
The best-case scenario for this lockdown is that it lasts three days only because there is no further spread and that genome testing will link the positive family to a Covid case which has been picked up in the three tests given to arriving passengers in managed isolation.
That would maintain the country's confidence in the Covid response.
A worse case would not only be the spread of cases but an inability to show through genome tests where the virus came from.
Locating the source of the infection is the key to stamping it out. Not knowing is likely to mean a longer lockdown.