Iranian women have been defending Sydney Sweeney for showing her body in a recent, controversial advertisement for a sports-betting company. They have been asking a rather obvious question: if her body belongs to her, why should an Iranian woman not be granted the same right?

That question appeared in the Persian comments under a news story about the advert. I was struck by how quickly the discussion moved away from the advertisement itself and towards something much closer to home. One Iranian woman wrote: ‘I’m a feminist. What’s wrong with her showing her body like this? It’s hers, and we shouldn’t mix sport and modelling.’ Another woman wrote: ‘The problem these Western feminists have with Sydney is that she’s sexy. So, what’s wrong with someone who is sexy and beautiful showing herself?’

There were dissenting comments, of course. But these caught my attention because they were not really talking about Sydney Sweeney anymore. They were talking about a principle that is much harder to contain: a woman has a body, and she should have some say over what she does with it.

For an Iranian woman, this is not a theoretical issue. Even as a man, this question follows you into the street. I can see it at the entrance to the metro, where a woman notices a patrol and has to decide whether to pull her headscarf forward or simply keep walking.

You see it in shopping centres, where women with uncovered hair move through crowds while women in chadors watch them. You see it at cafés, where a woman in a crop top can sit with her friends and order coffee while knowing that, in another place or on another day, somebody might decide that her clothes are a problem. You see it at universities, on the streets, outside concert halls and in queues, where women wear short skirts, sports leggings, short-sleeved t-shirts, dyed hair or red hair and, increasingly, simply dress according to what they themselves want to wear.

None of this necessarily looks like a political protest. But once the authorities have decided that these ordinary choices are matters of public morality, the clothes acquire a meaning that the woman herself may never have intended.

She can then make a very simple decision: she can co-operate with the authorities, or she can decide that she is not going to organise her entire appearance around the possibility that somebody else might object. That decision can be as small as walking past a patrol without pulling her clothes into place. The patrol may watch her. Sometimes it may stop her. Sometimes, especially in a crowded place, it may hesitate. There may be too many people around, or the confrontation may simply not seem worth it. A shopkeeper may choose not to intervene. A café owner may decide that what his customer is wearing is none of his business. Another woman sees this and realises that something that looked completely impossible a few years ago can, in fact, be done. Then she does it too.

This is how a rule can remain written down while becoming harder to enforce in everyday life. Nobody has to announce that a new political movement has begun. People simply keep making the same small decision, and the authorities have to decide, every time, whether they are actually going to enforce the rule.

This rule even applies to men: I recently became confident enough to wear shorts outside in Iran. This is not normally how a grown man expects to describe a critical moment in his political development. I did not join an underground organisation. I did not cross a border. I merely put on a pair of shorts and went outside.

Yet I still spent an embarrassing amount of time thinking about it. Would people stare? Would somebody say something? Would I suddenly become painfully aware of my own legs every 30 seconds? Would I regret it five minutes after leaving the house? Nothing happened. I bought something, walked around and came home. My knees survived. What stayed with me was not the shorts themselves but the amount of time I had spent imagining that somebody else might have the authority to decide whether I should wear them.

That is the part of the Sydney Sweeney discussion that I think is easy to miss if you look at it only as an argument about advertising, celebrity culture or Western feminism. The Iranian women defending Sydney Sweeney did not say that every woman should dress the same way, or that showing more skin is automatically liberating. They said something much more ordinary: if it is her body, she should have a say in what she does with it. That argument travels surprisingly well. It travels from an advertisement on an American screen to an Iranian woman’s decision about her headscarf. It travels from a celebrity’s outfit (or lack thereof) to a crop top in a Tehran café, from a model’s body to a woman’s uncovered hair on the metro, or to a pair of shorts on an Iranian street.

Somewhere along the way, ‘sexy’ stops meaning simply attractive. It starts to mean a body that is no longer waiting for permission. A woman who can wear the crop top, dye her hair, go to the concert, dance, walk past the patrol, sit in the café and carry on with her life. Not because every one of those acts is a revolution, but because sometimes the most direct way to push back against a tyrannical rule is simply to stop arranging your everyday life around it.

The authorities may think that giving people a little more space will make them more comfortable with the rules. People may instead discover that the space belongs to them, and that once they have learned how to use it, they are not particularly interested in giving it back.

No doubt Sydney Sweeney knew her advert would cause controversy in the US. Did she have any idea that would resonate so much with the beleaguered people of Iran? Either way, we can be grateful that she has reminded us what the freedom to choose looks like.