As a general cultural rule, it’s simple: guitars turn grown men into teenagers. Think of Paul Allen, the co-founder of Microsoft. While Bill Gates sets up a worthy foundation to find a cure for malaria, Allen splashes his millions on a Jimi Hendrix museum for Seattle and a massive boat in the Med to tempt the members of U2 to come and hang out with him on holiday.

What has Davis Guggenheim, director of An Inconvenient Truth and a forthcoming documentary on Barack Obama, decided to do with his newfound power? He has decided to invite Jimmy Page, Jack White and U2’s Edge to sit round and have a jam together so he can film it. At one point in It Might Get Loud, Guggenheim bashfully beams of Jack White: “He wrote a song right there in front of me, something I’ve never seen before.”

These days, our fêting of musical gods has taken on a new twist with the coming of Guitar Hero, the computer game where you score highly for rocking out in the same fashion as your idols. Guitar Hero III sold 8 million units at a whopping £39 each and was the bestselling computer game worldwide of 2007. It sold $100 million dollars of games in its first week of release. It grossed around $1 billion in total. When Guitar Hero 4 comes out later this month, it is expected to break all records. And this is a game based on simply pretending to play the guitar.

Guitar Hero scores you high for signature rock-star moves. “The whole concept is taking something everyone did as a kid, standing in front of the mirror with a tennis racket and pretending to play along, and making it something that actually lets you interact with the music,” says Tim Vigon, the manager of the Streets and the Zutons. “I know where all the chords are on a real guitar, but I can’t make it sound good, so with Guitar Hero for a moment I get to feel that feeling, like I’ve got the whole band behind me.”

But for the real-life guitar heroes whose songs appear on the game’s stellar soundtrack, onstage strutting is only part of the story. In a new series of films on the guitar the professed non-guitarist Alan Yentob gets some wonderful admissions from his subjects. Slash, the lead guitarist of the heavy-metal luminaries Guns N’ Roses, tells him: “The personality that chooses guitar playing seems to have a hard time expressing their feelings.”

Certainly, people begin learning the guitar for many reasons. Attracting women and being Jimi Hendrix are just two of them, but eventually the guitar’s sheer resistance to being played will wear down the faint of heart. It’s not an instrument for wusses. Tim Brookes, the author of a history of the electric guitar, quotes Ed Gerhard, the finger-style guitarist from New Hampshire: “You start off playing guitar to get chicks and end up talking with middle-aged men about your fingernails.”

Yentob’s documentary reveals that most of the great players he talks to were still young kids when they became obsessed with guitars. Mark Knopfler talks about how he stood outside the guitar shop for hours at a time; Matt Bellamy of Muse talks about seeing Hendrix at the age of 11; and Johnny Marr says his mum could safely leave him in the guitar shop when he was a tiny kid while she did the grocery shopping. These boys were still at primary school when they first saw and coveted a guitar. It was a friend, something to hold, a focus for that boyish energy and focus.

When I was little, my dad, Pete Townshend, spent hours of his precious free time when not playing with The Who photocopying chord symbols to make a lefthanded instruction book for his awkwardly-gifted daughter. But although I can play the guitar, I’m no guitarist. It was my good friend Morgan, the son of the Sixties songwriter Billy Nicholls, who had that unremitting energy and focus that it takes to become a proper guitar player. He started off one Christmas painfully picking out chords; by the spring, he could manage a passable Jimi Hendrix. His obsessive approach was one of life’s earliest lessons for me: people who really wanted to acquire a skill did not sit around. Today you can see him on stage at Muse gigs, triggering the wall of sound that cushions Matt Bellamy’s demonic guitar sound.

Aiming to demystify all of this, though, is missing the point. There is a real mystery to it. A great guitarist, like a great athlete, makes the distances look small. Eric Clapton would play solos on stage balancing his cigarette underneath the headstock and taking drags in quiet moments. This kind of ease with an instrument is testament to a life lived with it. Even the musicians can’t really say what’s going on. The guitarists in Yentob’s films reveal themselves to be curiously inept at explaining what really matters about their craft. Marr’s charming inarticulacy speaks volumes: “Playing the guitar, it feels more natural than talking.”

For all of them, though, it’s that matter of expressing individuality. My dad says: “There’s this idea of learning to play just like Jimi Hendrix, it’s still around in all these guitar magazines with their transcriptions, and I just think ‘why?’ There are different kinds of guitar players. There are those who want to play the songs exactly like the record, and then they’re happy. And there’s others like me who want to know how the songs are made, the structure, the chords.”

And sometimes even the guitarists themselves are foxed. The guitar technician Alan Rogan, who has worked for The Who and the Rolling Stones for more than a quarter of a century, tells the following tale: “Andy Fairweather-Low [the founder of Amen Corner] was a huge fan of Ry Cooder. He bought a plane ticket, went to America and said: ‘I’ll drive you, if I can learn how you do it.’ When he came back, all Andy could say was, Ry has these guitars, these Japanese pieces of junk, they seem like they are just on the brink of falling apart. But the sound he gets out of them, it’s like he touches them and something happens, I don’t know how he does it.” In the days of Guitar Hero’s strange mathematical ratings, it’s comforting to hear that at least some ways of scoring on the guitar remain utterly mysterious.

Imagine – The Story of the Guitar is on Sunday at 10.15pm on BBC One

Explore Music

• CD Reviews

• Live Reviews

Editor's choice

• The 100 Best Films of 2008
• Hitler and the Downfall mash-ups
• Britney Spears: The Circus