Leonardo DiCaprio loves the "eternal sort of mystery" that surrounds movie making.

The hugely successful actor says it is the unpredictable nature of film that really fascinates him. Despite his lengthy career, he still hasn’t got to the bottom of what makes a picture a hit.

"It’s always an eternal sort of mystery in making movies, and that’s the great fun, challenge, and excitement about doing what I do," Leonardo told August Man magazine. "As an actor, I do everything possible to tell a great story in a truly artistic way, but at the end of the day you never know how critics and audiences are going to respond."

The Titanic heartthrob discussed how he feels about getting older in the entertainment industry. The 38-year-old addressed the fact he is turning 40 before too long, and says he sees it as a milestone to reflect on his achievements.

"I guess the big 4-0 hasn’t entered my consciousness yet. I believe it’s very important to look back on the choices you’ve made and re-analyse where you want your life to go and the things you want to do as an individual," Leonardo pondered. "I came from a lower middle-class background where, for me, being an actor never seemed like an achievable dream. Once I got my first opportunity to work on a movie, it’s really been a mad rush to fulfil that dream."

Leonardo stars in the highly-anticipated film The Great Gatsby and has no plans to slow down his work commitments as he faces his future post 40.

"My goal is to keep doing great work… I haven’t stopped yet and hopefully the work will never stop," Leonardo continued. "While I’m here, I will always have that drive to not only produce great work, but to make a difference in the world.”

If the movie role offers do dry up, the actor has his environmental work to focus on. He aims to do more campaigning to promote green causes in the future as his concerns about the world grow.

“In my adult life, my environmental work and activism remain a priority. I created a foundation that focuses on raising public awareness of the very important issues concerning our planet, our environment, and the impact we as people have on the world we live in…" Leonardo finished. "It is not only an extremely fulfilling and gratifying learning experience, but has also taken me to some of the most interesting and beautiful places in the world.”