Exercising discipline, in the punishment sense, can be one of the trickiest tasks for any party leader, especially a prime minister.
It would perhaps help if each prime minister left the next one a set of "sentencing guidelines" because relativity is important, if not between governments, certainly within them.
The test is: "Is it fair?" And the test needs to be satisfied for the voter and for the party.
In the case of Clare Curran, she has been demoted from inside cabinet to outside cabinet and lost two of her four portfolios including open government.
The crime was not just giving a wrong answer in a written parliamentary question by failing to declare a meeting she had with a particular person.
It was failure to do the absolute basics - record her meeting with a prospective candidate for the role of chief technology officer, Derek Handley.
There were two aggravating features: she was Minister for Open Government, and this meeting was anything but open. It was also a second offence, having failed earlier this year to declare a meeting she had with Carol Hirschfeld which ultimately cost the broadcaster her job.
In both cases, it was not the meetings themselves, it was the false information given in written answers about meetings she had had. In both cases, the plea in mitigation from Curran was that they were genuine oversights.
Prime Minister Jacinda Ardern does not want to set the bar too low. She does not want to demote a minister every time a wrong answer is given. But she does not want to tolerate sloppiness over basic ministerial behaviour, especially not highly valued ministers.
Phil Twyford lost his responsibility for the Civil Aviation Authority of New Zealand when he was investigated for using a cellphone on a plane after the doors had closed. And he got it back. That was proportionate.
Clare Curran's punishment is proportionate as well. Sacking her completely would have created issues of relatively for future ministerial "crimes and punishments".
Not punishing Curran at all would leave Ardern open to claims she was going soft on her former flatmate.
It goes without saying that Curran is on a final warning.
But it may be that her fate is already sealed. Her harsher punishment may lie ahead in 2019 or 2020 when Ardern has her first reshuffle.