If I’m going to write about a film that has made a particular impact on me, there are a few I could mention. I could bring up the time, a few years ago, when I first discovered The Phantom of the Opera and duly became so obsessed that I watched it every week, without fail, for approximately four months. Or I could tell you that, whenever I now imagine my hopefully-one-day wedding, the image in my head is taken almost shot-for-shot from Mamma Mia! (donkey included). Or I could, of course, go into a great detail about the amaranthine existential crisis thrust upon me by The Truman Show, which has left me perennially unable to shake the feeling that my life, too, may be a cruel farce, contrived purely for the viewing pleasure of the general public. (If you ever happen to catch me brushing my teeth on some obscure satellite channel, please do let me know.)

But for now, it’s Erin Brockovich, that glorious true-story film which, almost single-handedly, stirred me out of my youthful apathy into the mindset of a wannabe activist. It taught me that, if Erin can do it, I can damn well do it too, whatever that ‘it’ may be. After all, she's a single mum with no job, three children to feed and mounting debt. And let’s not kid ourselves that society is kind to single parents because it's not. Nor is it kind to the unemployed or the poor. She’s an underdog in pretty much every way so the chances of her ever landing a steady career – never mind taking on and beating a huge corporation (oh, and getting justice for hundreds of other underdogs at the same time) – are low to say the least. But she does it. She does it by not taking no – that word she must have heard so many times in her life – for an answer. She does it by believing that she needn't rely on those who have always put her in the corner to get her where she wants to go. And she does it by refusing to accept that her life as it is now is how it always has to be. What better message could there be than that?

But there is, of course, another, glaringly obvious way in which Erin Brockovich is an underdog: she's a woman. This is a film that SMASHES the Bechdel test (that is, the set of pathetically minimal standards – namely, the inclusion of at least two female characters who talk to each other about something other than men – which, astoundingly, manages to catch out the majority of Hollywood). While there is, indeed, a love story in there somewhere – Erin strikes up a relationship with her next-door neighbour, George – take it away and the fundamental structure of the plot remains basically the same. It's almost as if women can do things independently of men… Weird, I know.

Some may call Erin Brockovich a classic rags-to-riches story – a fairytale of the modern era, even – but they sell it considerably short in doing so: it’s only really rags-to-riches if you acknowledge the huge-ass twist. After all, this is no Cinderella. That’s not to say there aren't similarities though: if we were to go all metaphysical on this, we might consider the ugly stepsisters to represent the society that repeatedly shuns Erin. But, really, the two stories are completely and fundamentally different: while Cinderella’s transformation is about appearances, material value and, ultimately, a man, Erin’s is about confidence, self-esteem and justice. And she don't need no man for that.

Thus, we find in Erin Brockovich that rarest of things: a truly positive screen role model for women and girls. She scales amazing heights, against all the odds, and, as her dry remark at the end of the film indicates, she does so without giving 634 blow jobs, which is always nice. The real-life translation of this is that Erin’s character demonstrates that it really is possible for a woman to achieve something on her own merit, without her appearance or sexuality coming into it. That may sound basic – and it absolutely is – but it's a truth that seems to have been forgotten. Or perhaps never even learnt. And Erin Brockovich goes some way towards remedying this, for which I will be eternally grateful to it.