What are we to make of John Key's bombshell? Reactions will obviously vary according to the political views of those making them, but his statement should be taken - initially at least - at face value. We should all understand the pressures that public life imposes, particularly on the major players. Living in the limelight is not by any means as much fun as it seems.
The Prime Minister may have been feeling the effects of a strenuous by-election campaign in Mt Roskill, and defeat there may have offered a glimpse of what a general election defeat might feel like. He may also have been at a low ebb, perhaps disheartened by the election of Donald Trump and what that has meant for the TPPA; he may have felt very keenly the loss of what was very much his own pet project.
It may simply be that he felt that he had done all that he could and that, as he himself says, he had "nothing left in the tank". And perhaps he sees the advantage, in terms of his legacy, of retiring while still on top and undefeated, rather than running the risk that the voters will tell him next year that it is time to go.
British politician Enoch Powell once famously said, with pardonable and only slight exaggeration, that "all political careers end in failure". John Key may not have been familiar with that well-known quotation but he may still have been tempted to disprove the wisdom it claims to represent.
Whatever the truth of such speculations, there will certainly be many well-earned tributes paid to him and his record of success as a vote-gathering political leader. He has undoubtedly been one of the most successful and popular of our prime ministers - though, it must be remembered, that despite the impression often peddled by National party acolytes, only one in three eligible voters actually voted for him and his government in 2014.