The most vital film of the year did not win Best Film BAFTA

Nobody really cares who wins the Bafta these days, do they?

It's just a bunch of impossibly wealthy, self-regarding people, flaunting themselves and making out that what they do actually has some relevance to the universe.

And yet.

I was pleased to see that Joaquin Phoenix won the Bafta for best leading actor because I think the film he made was important and, although I pretty much hated watching it from start to finish, it was far and away the best and most thought-provoking film I have seen in the past year.

Sam Mendes' film 1917 won of course, a safe bet because he did something a bit radical with the camera (following the soldiers' every move so that the action appears to be in real time) and it celebrated the quiet heroism of the ordinary man in the First World War.

But, apart from the camera trick, hasn't that all been said and done before? Noble, certainly, and if you've never seen a First World War film before, then no doubt affecting.

But I have seen many First World War films before, All Quiet on the Western Front has never been bettered in my view, and Mendes' film wasn't saying anything new. I took a packet of tissues but used none, I think because there was never really any sense of surprise or jeopardy.

You knew the leading actor would make it through. His bravery was impressive, remarkable even, but really this was Sam Mendes being given a lot of money to make a film to honour his grandad and as someone who worshipped the ground their grandfather walked on, one thing I have learned is that however much you think your relative to be remarkable and wonderful, no-one else really wants to know!

Meanwhile, Renée Zellweger won for her Judy Garland impression. Jane Horrocks can do that too and so can a lot of other people. Zellweger was great - but her work, unimportant. The film, about a film star whose gloss was fading, was no doubt a fascination in navel-gazing Hollywood, but it added nothing of real value to the wider world.

But The Joker does.

It is horrible to watch. Phoenix is largely repulsive and in the first half an hour, I really wanted to turn it off.

Gradually though, I could see what was happening. Phoenix was portraying a man in the dark grip of mental illness and the reason I wanted to stop watching is the same reason that we turn away from people in the street who are barking at trees; the same reason we turn away from mental health as a society, the same reason we dismiss anyone who is acting a bit strangely with, "Ignore her. She's just a bit mad."

It is unpleasant, it is unsettling, and, because we feel powerless, it makes us recoil, walk away and wish someone else would do something about it, as long as that someone is anyone but us.

Phoenix embraced this head-on. His body is in a horrible state, he is in a constant state of agitation, his leg twitching 19 to the dozen, and he frequently bursts into uncontrollable laughter.

Yet, he initially observes the world with hope, wishing he could become a part of it, feeling love, trying to take care of his mother, but when he asks for help, he is repelled at every turn.

As a new take on the Batman franchise, this is radical; dispensing forever with the binary comic book convention of good versus bad. But as a treatise on the current state of our mental health services, it is a masterpiece.

The other day, a friend was telling me about a woman who was acting strangely. "She used to be so outgoing," she said, "she had a great job and was really feisty. But now she never goes out."

Another friend was talking about her sister. "She's changed," she said. "Her behaviour is really extreme. She has these mad outbursts. It makes everyone in the family feel really uncomfortable."

I know of plenty of people, including even me in the past, who have seen a bit of this when times are hard. Being pronounced mad is a very easy label when you act a bit "off", but a reaction you rarely see from anybody to such a scenario is, "I wonder why?"

The Joker forces us to confront that question.

Why did the Joker, arguably Batman's most despicable nemesis, turn out that way?

Because, we learn, it was only when he did a bad thing, in the cause of fighting back against the abuse he was suffering, that he gained any power. Once he had tasted that power, after a lifetime of impotence, he, perhaps unsurprisingly, didn't want to give it back.

Nobody wants people in the grip of mental illness to turn on those around them.

When this happens, as we often read in the newspapers, the reaction is savage.

"There was always something odd" about him or her, people say, before moving on in relief that nobody turned on them.

Meanwhile, nothing is done. Nothing changes, and more people in pain go under the radar, for us to be shocked when they finally break out and do something that erases our blindness, if only for a single day, and for which we blame nobody but the person who flipped.

This film suggests what can happen when you spend a life being dismissed and ignored.

That is why I felt it was truly important and very much of the Zeitgeist.

When you call someone "mad" or don't like their behaviour, you write them off and demand that THEY change - when actually perhaps it is you who should.

And anyway, almost always, "mad" really means "I have something very dark buried and I am just waiting for somebody to ask the right question".

Let The Joker, and Phoenix's meaningful performance, be a reminder to ask it now.