If you have a spare two hours and twelve minute, check out ‘Cobain: Montage of Heck’. It’s a powerful documentary, directed by Brett Morgen, that gets all the way in on the legend of Kurt Cobain. Well, not quite all the way. But close enough that it’s not your usual estate-authorised documentary that only exists to further the mythology of genius (most often coz there’s a new greatest hits compo coming out). Montage of Heck doesn’t do that, if anything it personalises the man, not glorifying him but empathising with him.

Morgen gets face-time with most of the important people in this story. Courtney Love is there, Krist Novoselic is there, several family members are there. There’s extensive use of Cobain’s journals, home video and archival footage, plus some budget-stretching animated sequences (which will probably divide opinion, but they’re very cool). There’s a score by Jeff Danna that cleverly reworks some notable Cobain compositions into less familiar renditions. There are also a few too many home vid shots of Courtney Love’s tits than necessary, but whatever works.

One of the animated bits covers a troubling period of his teenage years, but it’s so weird that it doesn’t really seem true – no spoilers. Some deliberate attempt to show his troubled upbringing. It’s all built from recordings by Cobain, so take what you will from that. It’s the only really weird tonal shift in the film, though, the rest of it all flows determinedly from verse to chorus and back again as if Cobain wrote it himself.

It’s a very good film. Passionate Nirvana fans will obviously lap it up like a hungry dog but it works even if you only have a passing interest in the band. Morgen does a strong job of re-capturing the lightning that Nirvana captured in their own time, and the effects thereof.

Which begs the question: How exactly did Nirvana get so famous?

How did a band as loud, disruptive and heavy as this one find such mainstream success? It’s unprecedented. Like, not only does ‘Nevermind’ have child nudity on the cover, but it has tracks like ‘Territorial Pissings’ and ‘Stay Away’. Even ‘Smells Like Teen Spirit’… that thing is hard, man. Clichéd by this point in time, but damn hard. Nirvana built themselves on crunching, brutal riffs. Punk rock at its sludgiest, the kind of music that’s underground in its nature and that’s where it expects to stay. Yet somehow it didn’t.

Cultural booms tend to happen like a perfect an aligning of the planets. Right place, right time, right sound, right audience. Thousands of bands fell by the wayside into obscurity as Nirvana became the spokesgroup for a generation of slackers and rebels. Maybe the others peaked too soon. Or too late. Maybe they didn’t have the songs or the personality. The attitude or the beliefs.

The funny thing is, Nirvana didn’t really invent anything. They just amalgamated a bunch of different things into the beast that became grunge. Dynamic volume shifts, verse/chorus/verse/chorus/solo structure, the DIY thing, catchy melodies over heavy instrumentation, chequered shirts… it’d all been done before by some band or another. What Nirvana did was combine it all into an accidentally perfect package.

Listening back to a few of those records, you remember how great those songs were. How great those few albums were. How brilliant Cobain was, how crucial the bass and drums of Novoselic and Grohl were. It’s just hard to think that tens of millions of people at a time also thought all this. Nirvana ain’t your standard top 40 pop band. They didn’t pander or soften their message like most crowd pleasers. In fact, the whole thing with alternative music is that it’s supposed to be the exact antithesis of all that. It’s like they went full circle.

Of course, Nirvana had one thing that most bands could never match. They had Kurt Cobain. A fascinating, brilliant, tragic frontman. It’s easy to slight the legend that he became, especially in the wake of so many imitators. Look at that terrible Mark Wahlberg movie, or that other (not as terrible) Michael Pitt one. Or the numerous bands that emerged post-Nirvana trying to re-bake that cake. Cobain’s become less of a man and more of a myth.

But then you watch the legendary Unplugged show. A man sits up front, hunched over an acoustic guitar. Torn jeans, green cardigan and converse sneakers… straggly blonde hair spilling over his shielded face. Cobain didn’t just create music, he created a generation-defining aesthetic. He had this magnetic presence that comes across even in pixelated youtube concert footage. That feeling that you get when you’re close in person to some celebrity, this guy has that same appeal on video. His image is so iconic now that just to see him move/sing/ play/speak/live/breathe on stage is magnificent because it’s evidence that this was a real person who once existed among us. He was magnetic in the way that only the very greatest actors, musicians or athletes can be. In a way that is perhaps no longer possible in our social surveillance state times.

You could argue that Nirvana’s success broke the mould so badly that it’s never been fixed. They launched a niche musical movement into the mainstream, allowing for the whole grunge thing to be recreated, reimagined and redesigned into our culture. It’s a thing that happens all the time now in the modern age, where communities are able to find each other without the need for big business handouts and nudges. A fragmented world where your new favourite band and all that goes with them is just a click away. Any fresh sub-culture is only tweet away from becoming a fully formed movement.

All of that is why we’ll probably never have another Nirvana. We’ll probably never have another band as loud and abrasive as that to headbang to in unison. There are too many bands inspired to follow, too many small audiences now used to getting what they want (power to the people!). The musical marketplace no longer meets on a Saturday morning at the town centre, it’s personally delivered to our doors at our own command.

But I still don’t get how they got so famous.