THE MOST important rule in politics, the electoral equivalent of Occam's Razor, the clarifying maxim that should be displayed above the desktop monitors of hyper-active politicians, advisers and journalists in Westminster, is this:

Most things don't matter.

Almost all of the tactics, strategies, messages, campaigns, gambits, revamps, speeches, briefings, reshuffles and even policies that politicians and their advisers work on, and that lobby hacks analyse, are of zero enduring significance electorally. Very little of this political activity ever "cuts through" (in the Westminster argot) to voters, and even less of it manages to shift public opinion for anything but a few weeks. It is noise.

Elections are decided by a few fundamentals, such as the political cycle (the longer the government has been in power, the more hostile the public will feel towards it), the economic cycle (the more prosperous the country is feeling, the more likely they are to vote for the government) and, above all, the party leaders. Perhaps the only meaningful thing a political party can ever do to help its fortunes is elect a leader who has that "prime ministerial" quality that is hard to define but easy to recognise when one sees it.

Of course a party's economic credibility and closeness to the centre-ground matter, and these things are conveyed to voters via speeches, policies, campaigns, etc. But how well a party scores on these fronts is derivative, ultimately, of its leader. If a leader has a grasp of the national mood, and the will and the skill to reflect it, the party will be thought credible and centrist. If he does not, no amount of political activity by colleagues and advisers will compensate (in any case, if he is not a good leader the activity will be misjudged because the colleagues and advisers will be badly chosen).

Why am I telling you all this? Because it really, really matters that Ed Miliband, who gives his keynote speech to the Labour Party conference on Tuesday, is performing so appallingly in opinion polls, even though his party is (narrowly) leading the Conservatives. A Populus poll recently found that half of all Labour voters cannot imagine him as prime minister. On the eve of this conference, a YouGov poll for The Sun revealed that 5% of all voters think he is a natural leader, 4% say he would be good in a crisis, 9% regard him as decisive and 6% find him charismatic. Hours ago, a ComRes poll found that only a quarter of voters think Mr Miliband is a credible prime minister-in-waiting. Some of the reactions to him in focus groups are said to verge on the cruel.

Now, if you read my reaction to Mr Miliband's election last year on this blog, when I asked whether you could imagine a CNN newsreader referring to "British prime minister Ed Miliband", you will know that these numbers do not leave me on the floor in a daze of astonishment. I understood that the Labour Party found Mr Miliband warmer and more ideologically sympathetic than his brother, David, whom he vanquished to claim the leadership. But when it came to heft, bearing, judgement, decisiveness, star quality, appeal to swing voters, comfort on the biggest stages, and all the other characteristics that make a plausible leader of a nuclear power with a permanent seat on the UN Security Council and a population of 60 million....well, The Economist came to a different view to the Labour Party.

Still, "Most things don't matter" raises two questions. The first is whether a leader's (perceived) quality is immutable. The prime ministerial-ness of a leader may be one of the few things that matters in electoral politics, but is it something that can be developed, like a skill, or is it forged early on, like a characteristic? The evidence would seem to suggest the latter. Most politicians who have been elected prime minister in recent decades have seemed plausible occupants of Number 10 from the moment they became leaders of their party, especially Tony Blair and David Cameron. If Margaret Thatcher did not, it probably had more to do with the fact that Britain had never had a female prime minister before than because she was seen as particularly lightweight or unprepossessing. The opposite is also true: leaders of the opposition who were initially seen as not quite worthy of the big job tend not to dispel that impression over time. Ask William Hague, or Neil Kinnock. Ed Miliband, who is intelligent, in charge of a unified party and a better communicator than a year ago, must hope to win the public over in the coming years. But it may be that they have made their mind up about him, and that they do this with all leaders.

The second question concerns the exact balance between the few things that do matter. Does a prosperous economy trump a weak prime minister? Will a government that has been in power for a long time struggle to win re-election, even if the economy is booming? Labour don't need to do a huge amount to be at least the biggest party in a hung Parliament at the next election. If Britons feel poorer in 2015 than they did in 2010, could that anger not outweigh their doubts about Mr Miliband and see them vote out David Cameron? Again, the evidence is bleak for Mr Miliband. In 1992, the political and economic cycles were strongly against the Conservative government, which had been in power for 13 years and had just presided over its second recession in that time. But voters preferred John Major to Neil Kinnock as prime minister. That was enough to give the Tories a victory (and quite a comfortable one in the popular vote, at least). If you had to choose one of the three fundamental determinants of an election result to have on your side, you would opt for a top-class leader over a favourable spot in the political and economic cycles. When, if ever, has a party with a less esteemed leader than its rival won a general election?

Of course, you can draw all kinds of bold inferences from this analysis: that the Conservatives are in power simply because they have David Cameron, who strikes voters as more prime ministerial than anyone else of his political generation; that Labour would have eked out a fourth term in power had it not got rid of Tony Blair; that the result of the 2015 election was more or less determined on September 25th 2010, when Mr Miliband rather than his brother was chosen to take on Mr Cameron. Bold, simple-sounding and suspiciously reductive claims indeed. But are they wrong?