United Kingdom, Dec. 18 -- Colin Farrell is "fascinated with pain".

The 49-year-old actor - who has sons James, 21, and Henry, 15, from previous relationships - plays an addict in his latest movie Ballad of a Small Player and he explained he's drawn to roles exploring the dark side of life because all humans experience bad times.

Speaking to Jessie Buckley for Variety's Actors on Actors series, he said: "I have mad moments of joy in my life and joy in work and joy with my kids.

"But I've always felt that the common denominator in regard to experience as humans is pain.

"The one thing we've all felt, really, is pain. I put fear and uncertainty under that banner.

"Not everyone, sadly, has felt joy. And that's a great tragedy.

"But I'm...