Jack O'Connell learned to be less selfish making 'Unbroken'.
The 26-year-old actor lived on 400 calories a day and lost 30lbs to play Olympian and prisoner of war Louis Zamperini in the biopic and says his dedication to telling someone else's story was a very "maturing" experience.
He explained: "It was very maturing. I had to prioritise someone else - Louis.
"I had to prioritise his story over anything I desired at the time - diet and what have you. I got to know what it took to really devote yourself and not listen to the voice in your head that's selfish and ego.
"So that taught me a lot and that was a vital lesson and I feel more equipped having learned it."
Jack admits he learned a lot from his director Angelina Jolie, and though she has promised to always be on hand to offer him advice, she thinks he will be more "proud" if he steps away and makes it on his own.
He told Grazia magazine: "Angelina's definitely given me an insight into how to do it and do it properly.
"She's keen to remind me that if I ever need advice or anything [she's there] but I'm an adult and I've got a pair of b******s. I can stand on my own two feet and the more I do that, the more proud of me she's going to be.
"So I guess in that sense it does motivate me, but I don't want to cling on to the woman, you know."