Life isn’t fair.

And you know what? It can’t be.

Here’s the problem: The word “fair” doesn’t mean “justice” or “equity” or, indeed, anything very specific. Instead, it’s become a sort of all-purpose statement of moral superiority—superiority tinged, paradoxically, with victimhood.

Now, fairness does have an exact meaning in certain contexts. For example, if we’re playing a game, fairness means that the rules should be applied impartially. When we are kids and our parents and teachers set the rules, the word still has that essential meaning: it’s a young person’s way of demanding what we might call “equality before the law.” But as we get older, the word becomes more of a whine. In the mouth of a teenager—trust me on this—"it’s not fair" means, more often than not, “You won’t let me do something I want!”

In recent years, though, something odd has happened. Adults have started using the word in much the same way that teenagers do. More than in any previous generation, people today retain their teenage sense of self-centeredness. They use “it’s not fair” as a catch-all complaint, as an assertion of wounded entitlement.

Look at a Google graph of the use of the word “fairness.” From around 1965 it looks like the proverbial hockey stick—flat and then it suddenly shoots up.

We’ve developed a “fairness” obsession.

But what do we mean when we use that word? Do we mean “justice”? Do we mean “equality”? Do we mean “need”? Or do we mean something else?

Suppose you and Jane buy a cake together. You pay $6, and Jane pays $4. What would be the “fair” way to split it up? You could do it on the basis of proportionality—in other words, you get 60 percent of the cake and Jane gets 40 percent. Or you could do it on the basis of strict egalitarianism—half each, regardless of who paid what. Or you could do it on the basis of wealth. Jane has much less money than you for non-essentials like cake, so maybe she should get the larger share.

A case can be made for each approach. But the beauty of the word “fair” is that it doesn’t require you to come down clearly in favor of any of them. It gives you the cover of ambiguity.

So, for example, when a politician says, “We want the rich to pay their fair share,” he doesn’t usually mean that he wants the rich to pay taxes at the same rate as everyone else. He means that he wants them to pay extra. The word “fair” lets him present higher rates of taxation as a form of justice. But only if we don’t think about it too hard.

That’s the beauty of it. “Fair” doesn’t ultimately mean “proportionate” or “impartial” or “equal.” You can use it to mean almost any positive thing you like.

“I want fairness” generally means “Look at me—I’m a nice person.” Demanding fairness lets you tell the world how decent you are without your actually having to contribute a penny. It’s a kind of vanity: “Mirror, Mirror, on the wall, who’s the fairest of them all?”

Let’s get real. The only just way to distribute the cake is to see how much people are prepared to pay for their slice.

Sure, that could leave a banker with a bigger slice than a baker. Sure, we might not like that distribution. We might feel that the baker is doing something more valuable than the banker. He is making delicious pastries, while the money man doesn’t seem to be making anything—except money for himself.

But how can we judge someone else’s economic worth? You might want bakers to be paid more than bankers. I might want teachers to be paid more than movie stars. Since we all have our own preferences, the only way to measure the economic value of a service is to see how much others are prepared to pay for it.

That’s what the market does: it aggregates our preferences. It doesn’t ask us, in the abstract, what we think someone else deserves. It tests, in reality, how many hours of our own labor we are prepared to put in in exchange for a product or a service.

Under every other economic system, our relations are mediated by accidents of birth and social caste; financial rewards are determined by favoritism. The free market alone gives everyone the same rights. My money is as good as yours.

You can’t get fairer than that.

I’m Daniel Hannan, president of the Initiative for Free Trade and author of Inventing Freedom, for Prager University.