Opinion - So it's official. We know nothing. John Key has explained his resignation by saying he had "nothing left in the tank", and it's tempting to say the signs have been there. His listless approach to the Mt Roskill by-election was only the most recent example of a less-than-full commitment to the cause.
But Key has always been like that. Wonderfully relaxed, if you support him; maddeningly indifferent to pressing problems, if you don't. No one saw this coming. No one thought he would resign, not this year and not next year either.
It's probable he decided to go some months ago, but Mt Roskill got in the way of an announcement. We've known for months there would be a by-election and it was smart of him to wait till after it happened. Key and his inner circle would not have wanted the Mt Roskill vote to become a referendum on a new prime minister.
So why is he going?
He's said many times he would seek a fourth term. Did he change his mind or was he misleading us? Telling a necessary lie, like what parents tell their kids about Father Christmas: everybody swears commitment to their employer until they resign. There's no other way to do it.
But that doesn't feel right. Key has always tried to say what he thinks and to keep his word. If he'd led the party into the 2017 election and resigned halfway through the following term, no one would have thought the worse of him. Surely, until some point this year, that was the plan.
An existential crisis of the kind suffered by David Lange? Doesn't quite seem his thing.
A crisis of conscience, then? He's got one minister refusing an inquiry into the abuse of children in state care and another who keeps picking fights with teachers and school communities. He's got half the Cabinet floundering ineffectually in the face of a severe housing crisis...
Nope, it's not credible those things keep John Key awake at night.
A crisis in the family? That's possible. But if it comes down to Max Key needing a father - there's good evidence, after all - he might find he's a little late. For better or worse, Max is grown up now.
Maybe he couldn't stomach the idea of playing golf with Donald Trump, because cheating. Maybe it's just no fun anymore without Richie McCaw around.
The generous explanation is that, as Key himself says, he's got nothing more to give. Better for him to go now than struggle more listlessly than ever through a whole election year. They've got good numbers coming on the economy, the opposition is polling poorly - it's hard to think there would ever be a better time for him to step down.
The less-generous explanation is that after eight years as prime minister he's got bored, so he's off. He's not leaving any reform projects unfinished because he hardly started any - and those he did tended to fare badly anyway (the flag debate springs to mind).
John Key has spent his time as the most popular prime minister in our history... trying to be the most popular prime minister in our history. If that's truly all it was, it definitely makes sense to quit while you're ahead.
And yet he did a great thing for New Zealand. He made us feel good about ourselves. A sense of wellbeing infuses the national consciousness and a lot of that is down to him.
True, it's not universal. Hundreds of thousands of New Zealanders, far too many of them children, have missed out on the wellbeing.
To the left and right, Key has infuriated people who wanted reform, who wanted a long-term perspective and a coherent strategy, who wanted the PM to stand up more clearly for what he must know to be right.
But John Key wasn't interested in any of that. What he did, instead, was reassure us. And that gave us the confidence to be ourselves and not to feel the world was against us.
This is no small thing. Confidence is what enables everyone - from shop assistant to business tycoon, farmer to countercultural musician - to go about our business and our lives. It wins elections. Key has always understood this.
Not so long ago, it might have been counted a small achievement. This year, as we've witnessed the appalling unravelling of civil society in the United States, the value of his reassuring leadership has been made profoundly clear.
John Key is an Obamaite and we should be grateful for it - even if he does lack the actual political philosophy or purpose of Barack Obama.
Now it's game on. We're going to have a fiercely contested election.
And the task, for Key's successor and for the leaders of all the other parties, is this: to build on the good feeling we share about being New Zealanders with programmes to address the wrongs we still endure. To appeal to our Obamaite best and not our Trumpian worst.
* Simon Wilson is a journalist who specialises in politics and urban issues.