Whilst I was away, the Times named George Osborne as its Briton of the year because he's "set the terms of political debate." This corroborates my prior belief that political reputations depend heavily upon luck.

To see what I mean, imagine that we hadn't seen productivity stagnate in recent years and that instead GDP per worker since the 2010 election had grown at the same 2.1% annual rate that it had grown by in the previous 30 years.

In this scenario, if output had grown by the same rate that it actually has since 2010, there would now be 1.85 million fewer people in work than there actually are, and employment would be 869,000 lower than it was when Osborne became Chancellor. If half those 1.85m were measured as unemployed, there'd now be 3.3 million unemployed - a record level.

This alternative world wouldn't be all bad: it would be one in which productivity growth had raised real wages and so there'd be no cost of living crisis. Nevertheless, it would be catastrophic for Osborne (though given the psychological cost of joblessness, this would be the least of our concerns.) His prediction that the private sector would create enough jobs to offset public sector cuts would be proved false, and the anti-austerians predictions of three million-plus unemployed would be correct.There'd be no "partial vindication" of Osborne. He'd be obviously wrong.

However, the fact that he has escaped this fate is pure luck. The causes of the productivity stagnation are obscure, but nobody believes Osborne's conscious policy decisions loom large among them. Neither Osborne's supporters nor detractors think he is responsible for flatlining productivity. And they are right.

In this sense, insofar as Osborne still has any sort of political reputation, it is thanks to the good luck of stagnant productivity.

In saying this, I don't mean that Osborne is uniquely blessed. I suspect that Thatcher's high reputation on the right is due in part to luck. And for years New Labour had the good fortune of a mostly benign global economic environment. Instead, my point is merely that in politics - as in life generally - luck plays an enormous role. Curiously, the rich and powerful, and their lackeys in the press, underplay this fact.