Perception is reality. It's entirely appropriate that it was a political strategist who coined this phrase in the 1980s, and election campaigns ever since have been played out according to this tenet.
Lee Atwater, the man responsible for the phrase, worked on George Bush Senior's campaign in 1988, in which Bush turned round a 17-point deficit to claim the White House. Atwater died three years later at the age of 40 from a rare form of brain cancer, but his creed lives on for political strategists and marketeers alike. Forget the facts: if you can make people believe something, it becomes, if you like, a de facto fact.
It looks like our next General Election campaign, too, is going to be contested according to Atwater's law. At least that's what we can glean from the results of an Ipsos/Mori poll released yesterday. The poll, conducted in 14 countries, measures the difference between public perception and reality, and guess what? On some of the big issues in our world - immigration, unemployment and teenage pregnancies - most people form their opinions, and therefore cement their political allegiances based on a rather hazy understanding of the facts.
There's no question that immigration is going to be one of the most important and contentious issues in the 2015 election. The rise of Ukip - yes, they do have one MP, let's not forget it - has panicked the main parties in what may be seen as a race to the bottom as far as immigration is concerned.
A Martian arriving in the height of the campaign and immersing himself in our media might be excused for believing that it's the only thing that matters, as Tory and Labour candidates try to outdo each other in striking a tough stance on immigration.
I'm not saying that immigration is an insignificant issue for many people, but I think talk of being "swamped", and the amount of air time given to Ukip, creates a false impression of the effect it is having on the nation.
A perception exists that we are overrun by immigrants (in a recent poll conducted by the same organisation, 30 per cent of Britons identified asylum and immigration as issues more important to them than the economy and healthcare).
In pictures: Calais immigration crisis
In pictures: Calais immigration crisis
Anti-fascist activists confronted police in Calais. Hundreds of extreme-right activists demonstrated to "save" Calais from homeless migrants inundating the French port city in hopes of crossing the English Channel to Britain
A man hold a banner which reads "Migrants equal insecurity, unhealthiness and economic disaster" in Calais
French police and demonstrators eye one another in Calais
Migrants protesting in Calais, France demanding human rights protection, they have alleged police brutality against them, with some claiming to have suffered broken hands and legs
Migrants protesting in Calais
A 16-year-old Eritrean girl named Rita shows Reuters a fist-sized bruise on her upper arm where she said police had hit her with a baton as she sits outside her makeshift shelter somewhere in the woods, known locally as the "jungle", close to a chemical factory in Calais
Migrants sit on the stairs of a building in Calais
Migrants from Erythree and Sudan eat during a daily food distribution near the city hall in Calais
Migrants from Africa are chased by French policemen as they attempt to board lorries heading to Britain on the road to the ferry terminal in Calais
Migrants storm Calais port
So when the pollsters asked the British public what proportion of the population is Muslim, they answered 21 per cent. This turned out to be a wild over-estimate, based no doubt on Daily Mail editorials and Nigel Farage soundbites.
The reality is 5 per cent. This is a statistic that is unlikely to play a part in forthcoming political debate because it just doesn't suit the adversarial, fear-fuelled form of politics we engage in these days.
In the United States, these figures are even more stark, not terribly surprising given the amount, volume and prevalence of anti-Muslim sentiment over there. When asked, Americans thought that Muslims made up 15 per cent of the US population. The truth is just 1 per cent.
More Simon Kelner:
Talking about football helped me with my cancer recovery
My limerick response to Ukip Calypso
Sir Alex Ferguson crushed my dreams
Atwater was right. Public opinion, influenced and skewed by the self-serving interests of parts of the media and some politicians, is what we have to deal with. Prejudice can create a reality all of its own. How depressing.