Music legends especially so.
Fail to tune into the character, the voice, the instrumental skills and your career could be yesterday's grits.
So when the legend to be portrayed in a new stage play is country and western icon Hank Williams, you can understand why an actor offered the role would be excited - and a litter nervous.
Yet Sean, once of Harry Potter fame, (he played Oliver Wood) seems to embrace the idea of playing Hank in the way a good ole' boy would embrace a bottle of Lone Star beer and a curly haired gal dressed in gingham.
"It is a challenge, but one I'm really looking forward to," says the Maryhill-born actor of the Oran Mor production 'Lovesick Blues', written by David Bailey and directed by Dave Anderson.
Indeed, the life story of the singing cowboy could have formed the lyrics of an entire country album.
"Williams was, according to reports, a total maniac, a real Jekyll and Hyde character who would drink anything, including rubbing alcohol.
"But the music was fantastic, and when you do a play like this you have to remember it's the reason why most people will turn out."
Williams' life won't be hard to dramatise. Growing up in dirt poor Alabama, young Hiram, as he was then, was born with a form of spina bifida, his father suffered a stroke and the family's first house burned down, destroying all their possessions.
His mother was said to have bought young Hiram his first guitar with money she made from selling peanuts.
But the peanut money showed sings of paying off when the teenage Hiram met Rufus 'Tee-Tot' Payne, a street performer, who gave Williams guitar lessons in exchange for meals prepared by the youngster's mother.
Aged 14, the talented Hiram attracted radio station interest, and his career took off.
So too did his dependence on alcohol and pills, (said to be related to back pain resulting from his spina bifida). And his black temper failed to subside, the star capable of pulling a gun on people at the drop of a ten gallon hat.
Williams heart gave out when he was just 29, but by then he'd already released enjoyed 11 No 1 singles on the US Billboard chart.
"Hank lived the fist two acts of how the classic story is supposed to go," says Sean. "He should have died, overweight, at the age of 50 having lost everything; that's the usual country and western story. But he didn't get the chance."
How to play such a conflicted - but talented - character?
"I don't know yet," admits Sean, smiling. "It will come. But country and western isn't that hard to play. And Hank seems to have had a similar vocal range to me.
It's just a question of playing with the band, again and again, to get it right. Putting it across though will be the challenge, although the accent doesn't worry me. In fact, I rarely perform in my own accent."
Sean, now 31, has shown quite incredible performance skills since the age of ten, when he appeared in Iain Glenn's astonishing production of Macbeth, at Glasgow's Tron Theatre.
At 13, he appeared in the film The Winter Guest, directed by Alan Rickman, who recommended the boy from Maryhill to a London agent. But it was the Potter role which brought with it the premieres and crowds of screaming female fans.
Sean however didn't go down the Hank route. "I had been in the business for ten years, so it kept it in perspective," he says, smiling.
"How often do you see the story of someone achieving success so quickly - and then their life becoming a car crash. And remember, I wasn't one of the key players, or I may have lost it a little."
What seems to define Sean are the roles he's chosen. While ambitious, he's also clever and considered. He's never leapt into work in the hope it will bring fame and fortune, which is why he agrees to theatre roles such as the likes of last year's production Solid Air, playing guitar legend John Martyn.
"I worked on Martin's guitar style for a few months," he says. "That was a real challenge,walking on stage knowing I had to convince as Martyn.
Indeed, Biggerstaff has played several real-life characters, attracting great reviews for his BBC4 TV movie Consenting Adults, in 2007, playing Jeremy Wolfenden, which won him the Scottish Bafta for Best TV Actor.
Now, he's about to wear denim and a big hat.
"I was offered the Williams role after Oran Mor producer (the late) David MacLennan saw me perform blues in a Glasgow pub," says Sean.
"I never got the chance to thank Dave for recommending me."
Sean will give Hank his all, because it's a great story, and a great part.
"It's all about good work," he says. "There's nothing worse than walking on a stage to do something that's not worthwhile."
l Lovesick Blues: The Hank Williams Story, Oran Mor, July 31- August 2 and August 7-9