But every now and then you see a performance so far removed from the individual it defines what acting is all about.
Helen MacKay's first Oran Mor appearance highlighted she can indeed convince as someone she most certainly isn't.
The 27-year-old played a 16-year-old, ever-cussing schoolgirl with complete conviction in dark drama 3 Seconds.
Last year she also appeared alongside Elaine C. Smith in Saint One, and her role as an excited chip shop assistant revealed a huge talent for comedy.
Now, it's no surprise she's charged with playing a young, thrusting newspaper editor in Fishwrap, by Kieran Lynn.
It's the story of the problems in the newspaper industry, set in a small town, asking whether tabloid print will survive in the face of the tablet.
And asking what a young woman will do to hold on to a job.
"Caroline is 21, dead keen and fresh out of uni," says Helen.
"And she gets the chance to become the editor of a small newspaper in Alloa that's been taken over by a big company.
"But can she cope with the demands on her?
"And we discover she's up against traditionalist Thomas, (Ben Clifford) and her boss is Pauline (Louise Ludgate) who is backed by an oil company.
"It's a great play. And a great challenge."
There's no doubt it's one Helen MacKay will rise to. But why does she inhabit stage characters so effortlessly? Well, she makes a great deal of effort.
The actress is not prepared to be simply a performer. Each appearance on stage, she reckons, is an opportunity to learn. "I could spend my time when not on stage in the dressing room reading a magazine," she says, smiling.
"But that's not for me. When I'm not on stage I'm watching what goes on on stage.
"I'm learning from the more experienced actors. I'm looking at the production and trying to work out what makes it work. Or doesn't."
When Glasgow-based Helen landed a part in stage play Para Handy years back, the small role didn't contain her enthusiasm, her desire to learn from veterans such as Jimmy Chisholm.
When she starred in Cinderella at Christmas in Perth, she was so focused on producing the best possible show, she even suggested a change in one act.
MOST actors would be happy to coast towards the final run after 51 performances, but not this one.
"I realised that the audience were able to predict when Cinderella would transform into the beautiful woman who goes to the ball, so I came up with a bluff, whereby the audience were conned for a moment," she says .
"And it worked. I just wish I'd thought of it at the start of the run, but at least I got the chance to improve the moment."
Helen was once launched from the chorus to play the lead in the NTS production of Peer Gynt, even though she wasn't an understudy. Director Dominic Hill knew she knew the play.
She said: "Growing up in Thurso there wasn't a lot of scope but I went to dancing lessons from an early age.
"Then at 15, an Eden Court theatre outreach project came to town and my life changed. I knew I wanted to act."
Helen signed up with Scottish Youth Theatre.
She said: "Acting took over my life and so I worked in a little cinema, the box office, ushering, cleaning up popcorn, everything, throughout the year to save up enough money to do the summer acting courses."
Aged 18, Helen applied to RSAMD drama college in Glasgow. She failed.
But then failed better. And at the third attempt, she was in.
She said: "Each time I made it to the final selection, so I was getting closer. Then when I finally made it at 21, I was ecstatic."
She revealed huge promise. And incredible self-confidence. "At the end of my final year I was asked to join the graduate scheme at the Citizenss Theatre, but I turned it down.
She said: "I had the chance to appear in Silver Darlings with Kenny Ireland, and it was too good to miss.
"Yes, I had a year's work guaranteed at the Citz, but I really wanted to get out there and act, especially in the North-east."
Helen, who appeared in Rab C. Nesbitt's Christmas TV special, has grown beyond the North-eaast. In fact, she's the future of Scottish acting.
"I just love what I do," she says, smiling. "It's about storytelling, and I get to do that for a living."
l Fishwrap, Oran Mor, until Saturday.