Ashley Bloomfield says the theories Jacinda Ardern comes up with on the origins of the Delta outbreak are "usually good".
But he does worry she - not to mention himself and other experts - might have missed something.
The source of the SARS-CoV-2 viruses in Auckland has been traced back to the outbreak in New South Wales, arriving here via a flight early in August. Genomic sequencing has found there was just a single introduction - not multiple, like in last year's first wave.
Just how it got out of managed isolation and quarantine and into the community remains a mystery however. The Prime Minister told RNZ on Wednesday she's been lying awake at night trying to figure it out, and tells the Director-General of Health some of her theories.
"They're usually good ideas," Dr Bloomfield told The AM Show on Wednesday, and that they align with some he and other experts have come up with.
National Party leader Judith Collins, appearing on The AM Show before Dr Bloomfield, said she doesn't think about anything at night, and just goes to sleep - recommending Ardern do the same because "there's no point".
"I think if you're worried about something then either deal with it or accept that you can't change it. There's no point worrying, lying awake all night thinking about where the outbreak's come in."
Dr Bloomfield is somewhere in between - he'd like to know how it happened, but is also confident the public health measures put in place to stamp the virus out will work.
"Nothing keeps me awake too much at night, but I do lie there occasionally thinking, 'Is there anything we're missing at the moment?'
"But so far, thanks to a huge effort by Aucklanders and others around the country, alert level 4 is doing what it's supposed to do. Let's just hold our nerve."
Case numbers have started dropping, but he warned Wednesday's might go up after a round of day 12 tests of close contacts.
"The number may be lower, it may be a little bit higher. Let's just see. The key thing is it does look like we hit the peak a couple of days ago and we're heading in the right direction."