History always looks settled and determined when you look back on it. Ah, people say, Hitler was destined to lose the Second World War - his megalomania inevitably led him into Russia. Britain's wealth and international financial position doomed Germany to defeat in the First World War. Russia was 'always' going to be the country to experience communist revolution, hobbled by an unstable mix of nascent and uneven industrialization, stupid autocratic government and a large peasantry with apparently little to lose (who were eventually liquidated, but that's another story).
Don't you believe it. There are always alternatives, as one of my old tutors has always insisted. If historians can offer anything to public policy, it's to show just how contingent and confused most developments really are.
We're faced with this now in our politics, actually. The Prime Minister's smooth performance, good manners and rather laid-back approach to governance chime with voters - though his hands-off approach will bite him one day. He looks the part - one reason why Conservative poll numbers haven't moved much, while Liberal Democrat numbers have tanked.
All of this serves to convince many that it was always going to be thus - he was always headed for No. 10 against a knackered government and an unpopular leader.
But lots might have been different; had Labour got rid of Gordon Brown in 2009 (rather than in the absurd failed coup of early 2010); had the Party fought a better (and less cash-strapped) campaign; had the Prime Minister restrained himself before he insulted voters; had Brown reached out to Lib Dems rather than treating Nick Clegg with contempt. 2010 might also have gone differently had Chris Huhne defeated Nick Clegg for the Lib Dem leadership in 2008. It's difficult to see the now-Energy Secretary being quite so enthusiastic about a tie-up with the Conservatives.
The Conservatives' overall electoral position isn't as strong as it looks, as I've argued myself in print, and as many others have also pointed out. If their 2010 share of the vote had been a couple of points down, and Labour's a couple of points up, then Labour would simply have continued to govern.
Squint a bit - David Milliband in No. 10 with Nick Clegg as Deputy PM? Not as unlikely as you might think with hindsight.