The personal is political - and never more so than when you are Prime Minister. As Head of Government, you have a connection of influence with every New Zealand citizen, as well as non-citizens within New Zealand's borders and many more beyond. With that great influence - with that great power - comes great responsibility.
But this is something else that Key tended to fudge.
His most egregious episode was "ponytail-gate". Key was out of line: the waitress knew it, Bronagh knew it. Yet he seemed to believe that, at worst, he was no more out of line than any other bloke. This oversight was extraordinary - but it spoke volumes about his non-careerist conception of what it is to be a politician.
Usually this worked very well for him, electorally speaking, as he jovially appeared in the All Blacks' changing rooms in a black suit, the Big Gay Out in a pink polo shirt, and countless sausage-sizzles in between. But at times this "people's leader" went too far: too much "people", not enough "leader".
This had political implications, most notably his lack of decisiveness over systemic long-term problems like housing affordability, superannuation, income distribution, freshwater quality and climate change. These are issues that require tough choices, even unpopular choices, to achieve some greater good.
Key's short-termism was typical, if not exemplary, among his political cohort. But there's only so long that such problems can be waylaid - and the popular revolts are gathering apace.
International context is irresistible. Key's departure occurs amidst a rash of centrist leaders being turfed from their positions.
Indeed, the same day that Key resigned, Italian Prime Minister Matteo Renzi was conclusively snookered by a constitutional referendum that he called for and lost. Key was lucky that when he courted the public's contrariness by referendum, it was for a more trivial issue: our national flag.
By contrast, Key's friend David Cameron staked his prime ministership on a spectacular wager. He gambled the Union, the European Union, and Britain's place within the world, all to exercise discipline over a minority of Euro-sceptic MPs within the Tory Party's ranks. His loss has historical proportions.
Key also enjoyed good personal relations with US President Barack Obama. Obama served his two full terms, of course, but the election of Donald J. Trump still feels like an ousting, an intentful rejection of Obama's liberal elitism, his cosmopolitanism, his dignity and thoughtfulness, and his unpopular compromise with American financial and military power. What will remain of Obama's legacy after the Trumpocene?
The fates of his friends can't be absent from Key's calculations. A new political rationality is storming the horizon. The Trans-Pacific Partnership looks sure to be scuppered: a legacy unrealised and a lost investment of substantial personal and political capital.
The contingencies of politics have put the inevitable in doubt. So Key has chosen to commit political seppuku, to end it all in a sunny glade of enviable polling, while his peers are being crudely defenestrated.
A consummate player of the political game, Key may well realise that tried-and-true strategies won't still work if the rules of the game have changed. His abrupt departure, arguably his most decisive moment, might also be his most responsible. He has cleared the way for someone whose instincts could be better aligned to the times.
But it might not be so. Unexpected consequences could still lie in wait, especially if New Zealand's political stability is linked inextricably to John Key's personage. Is there a latent discontent throughout the country that will discover itself at the ballot box, prepared to choose the unknown over the familiar, the disruptive over the status quo?
Will Key's wager reveal that there are more dangerous things in this world than a triangulating centrist? Only time will tell.
