What happens when 95 per cent of people like something, but 5 per cent of people prefer something else?

You might think natural democracy would prevail: that the 5 per cent would acquiesce and go along with the taste of the majority. Not necessarily. In many cultural settings, it is common for a small, intransigent minority to beat a much larger, tolerant majority. If you’re hosting a dinner party, for instance, all it takes is one git with a spurious ‘fenugreek intolerance’ to veto your best lamb curry.

You might call this ‘the asymmetry of tolerance’, where certain social systems end up calibrated to suit their most inflexible component. If the majority prefers X but will tolerate Y, while a minority will only accept Y, what matters is not the weight of numbers or the strength of preference: intransigence carries the day.

Take your typical drinks party. One group of people have a strong overall preference for beer but are happy to drink wine (I will generally drink anything at a pinch, except retsina); however, 20 per cent of women (10 per cent of the group overall) will typically not drink beer under any circumstances. So at any mixed event, the host can get away with serving only wine. Wine is the Type O blood of alcoholic drinks; you can give it to anyone. The intolerant 10 per cent hence defeat the easygoing, beer-preferring majority.

The disproportionate ubiquity of certain foods can be explained by this effect. Pizza is a hugely successful food not so much because it is loved but because nobody hates it: even your picky children will eat it. By contrast, it is a risky venture to open a fish or steak restaurant: in any group of five or more people, there will always be one who doesn’t feel like eating fish or steak: their lone veto will prevail, and everyone will end up at Nando’s instead (chicken being the Type O-negative of the meat world).

As Nassim Taleb pointed out when he spotted this phenomenon, minority rule can prevail in many areas. Schools where only 5 per cent of the pupils are Muslim will keep halal kitchens, because it is assumed non-Muslims can be served halal food whereas Muslims will eat nothing but. All New Zealand lamb imported into Britain is halal, as is the chicken at Pizza Express. Almost all biscuits in Britain are now vegetarian (even Fox’s Party Rings recently capitulated). This process happens for the same reason most hospitals request Type O blood. It is far easier to stock and distribute something that can be given to everyone than to maintain separate -supply chains.

This seems to be a universal mechanism whereby a small stubborn group can beat large acquiescent ones. At times, it is a good thing: consumer boycotts can work even if only 10 per cent of people participate. This vulnerability helps keep companies honest.

But the same thing can be dangerous. The reason the principle of free speech has to be so staunchly defended is that it is vulnerable to abuse by minority rule. Once you let the idea take hold that something cannot be said because it might offend some imagined third party, you fast enter a death spiral of intolerance: demands for safe spaces, no-platforming, trigger warnings; a bizarre world where Peter Tatchell is deemed too ‘racist and transphobic’ to share your stage, say, or where comedians cannot perform on the university circuit because it is impossible to say anything funny without arousing censure from a tiny group of obsessives with invented grievances.

It is worth being alert to minority rule: it teaches that even when most people are reasonable, this does not mean that reasonableness will prevail. There are some principles which tolerant people have to be intolerant about.

What matters is not the weight of numbers or the strength of preference: intransigence carries the day

Rory Sutherland is vice-chairman of Ogilvy Group UK.