Man Utd's defeat on Sunday contains a warning for David Cameron - one he will almost certainly ignore.

I'm thinking of path dependency - the tendency for a small events to amplify into big ones.

For example, having gone a goal and man down on Sunday, Manyoo chased the game and so left space for Citeh to exploit, thus conceding more. This boosted Citeh's confidence and demoralized United, leading to more goals. A small edge thus ballooned into a large one. United suffered from this on Sunday, just as they benefited from it against Arsenal.

Citeh are not five goals better than United, any more than United are six better than Arsenal. In both cases, what we saw was that a small difference became a large one. Success breeds success.

We see similar things in the history of technology. The qwerty keyboard, for example, was not, initially, technically superior to others. But once it became widely used, it became even more widely used because it was what people had (arbitrarily) become used to. Bill Gates' detractors say a similar thing is true of Windows operating systems.

It might even be that the ubiquity of petrol-powered cars arose because an initially small advantage over steam cars led to greater investment in petrol engines and thus, eventually, to a massive superiority.

It's not just success that breeds success, though. So does failure. Rogue traders become rogues because they suffer early losses and then, in their desperation to break even, take on reckless gambles which sometimes fail.

What's this got to do with Cameron? Simple. There's another example of path dependency. Robert Cialdini describes how during the Korean War, American PoWs were asked by their captors to make mildly anti-American remarks. Having made such mild statements, some PoWs would then be easily induced to go further, with the result that they became collaborators. This happened, says Cialdini, because:

Once we have made a choice or taken a stand, we will encounter personal and interpersonal pressures to behave consistently with that commitment'many times a man would change his image of himself to be consistent with the deed and with the new 'collaborator' label, often resulting in even more extensive acts of collaboration (Influence, p57, 71)

Good salesmen understand this. They are keen to get small business from customers, because they know that these often lead to bigger orders.

Herein lies the danger for Cameron. The 81 MPs who defied the Tory whip yesterday have become 'rebels' or 'independent minds'. They might therefore behave like this in future. Having gone onto the rebel path, they might stay on it. Tory backbenchers will thus become harder to control.

So, why do I say that Cameron won't learn this lesson.?

It's because of another feature of path dependency. The event that puts us onto a path might be just luck. The mediocre product that is lucky enough to sell well might gain further custom. The team that is unlucky to concede a first goal might chase the game and be caught on the break. And if we are lucky to get a good first job, the training and opportunities it gives us will enable us to have a successful career.

This, of course, is just what happened to Cameron. He was lucky to have the family connections that got him his first job, and this put him onto a good path.

Which is why he'll not learn the lesson. To acknowledge the power of path dependency, Cameron will have to recognise that he owes his success to luck. But this he cannot do, as the privileged are no more capable of seeing their privilege than fish are able to see that water is wet.