A ten-year tenure as prime minister is enough, as Cameron rightly observed. Margaret Thatcher and Tony Blair had evidently lost touch with reality, to put it politely, by the time they had been in office so long. Cameron, already prone to hubris, is wise to want to escape.
There is, however, no chance that he will be able to serve a full second term. He isn't a president; the Tories will need a new leader for the next general election, currently scheduled to be held in 2020. Instead of quashing speculation that he might stand down after a 2017 in or out referendum on the EU, it seems likely to only intensify such talk. He will constantly be asked when he intends on standing down by any reporter lucky enough to be granted an interview.
And the timing is extraordinary. To announce his intention to stand down just weeks before a general election seems an utterly unnecessary distraction and might actually damage his electoral chances; do the general public want to vote for someone who already has his eyes on retirement?
In true football manager style, Cameron spoke of 'the Theresa Mays, and the George Osbornes, and the Boris Johnsons' who could succeed him. All likely candidates at this stage, certainly, but any successor would need a decent run-in time to stamp their mark on the party before a 2020 poll. And it's worth noting, both May and Osborne hold positions which are vulnerable to political weather and their stars could wane. As for Boris, whatever his personal popularity may be, he remains a liability.
Other potential successors will inevitably emerge. Liam Fox and Owen Paterson still seem keen to be champions of the Tory right wing but it's hard to imagine either could mount a serious challenge. And the trouble for these two - and for those mentioned above - is that they would have been at the top of their party for a decade or longer. Fresh faces may be required. And, as yet, it's hard to identify likely candidates from the modernising wing of the party. A shift to the right looks likely and potentially dangerous for a party that would have been in power for ten years by 2020.
In the event that the Tories find themselves in government after May, every speech or move made by any likely successor will be scrutinised for any hint of leadership ambitions. Inevitably, these moments will be over-read and misinterpreted. All this turmoil will only destabilise and fracture the party further.
So Mr Cameron should enjoy that glass of wine while he can: he may have just unleashed years of trouble for his party.