Twice in the past week the Prime Minister has had to discipline senior minister Phil Twyford.

On Monday, she said Twyford went too far when he called Treasury officials "kids fresh out of university" after they questioned his KiwiBuild policy.

This morning, she said she was "deeply disappointed" in him for making a phone call on a plane after the aircraft doors had shut.

The common theme in Twyford's two slip-ups is arrogance – a worrying trait so early in his Government's first term.

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It clashes badly with the kind, compassionate Government that Ardern wants to create.

Ardern conceded that she did not know whether it was obvious to the Transport Minister that he had broken civil aviation rules when it was raised with him.

It was Ardern rather than Twyford who fronted to media this morning. He apparently had to make a speech to a business audience in Henderson and cancelled his regular Friday morning slot on Newshub.

That does not necessarily reflect badly on Twyford. The Prime Minister is responsible for disciplining her MPs when they make mistakes, and it is up to her to explain why Twyford had to lose his civil aviation portfolio and why his resignation offer was not accepted.

Her sanction is appropriate. Former Prime Minister John Key also declined an offer from his former Transport Minister Gerry Brownlee in 2014 for an arguably more serious breach when he bypassed security at Christchurch Airport.

Like Twyford, Brownlee also delegated his Civil Aviation Authority responsibilities to another minister.

But the Government can't afford for one of its senior, high-profile ministers to get a reputation for being arrogant and overconfident.

As Housing Minister, Twyford is tasked with one of the Government's flagship policies - building 10,000 affordably priced houses a year. He has an unforgiving, relentless opponent in National's Judith Collins, who is seizing on every minor slip.

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There are already signs that Government's massive building programme will struggle to reach its targets, and the parameters are gradually being shifted as the reality of the housing market sinks in.

The Government will be asking for patience from voters as it gets Kiwibuild underway, and it will be needing a serious sales job by Twyford.

On the last week's evidence, he will need to find some humility if he is to take the public with him.