CANNES, France (Reuters) - Danish director Lars Von Trier unveiled his much-awaited Golden Palm entry at the Cannes Festival on Wednesday, "Idiots", a troubling and provocative story of a group of young people who pretend to be mentally retarded. Many festival-goers had placed their money on Von Trier's film for the top prize before having seen it, going on the originality and force of some of the director's earlier works, such as "Europa" and "Breaking the Waves". He is one of the most admired, yet controversial directors of his time. Unlike 1996, when "Breaking the Waves" was passed up for the Palm despite widespread prediction it would win, Von Trier has overcome his fear of flying to attend this year's festival. But on Wednesday he refused to appear at the press conference following the screening of "Idiots". The film is about a group of friends who behave like the mentally retarded, and in so doing discover their own inner selves as well as the hidden face of the outside world. Some see it as a game while others, like Stoffer, the head of the group, considers it an ideological mission and pushes his friends to the limits by daring them to behave like the mentally retarded in their home or work environment. Like his compatriot Thomas Vinterberg who is also up for the Palm with "The Celebration", Von Trier decries bourgeois stupidity and the cruelty of prejudice against those who are different. "There are two sides to idiocy. There's looking at an idiot and being an idiot. I tend to empathise with the idiot," Von Trier said. "Idiots" was shot in accordance with the strict diktats of Dogma, a charter the two directors created in 1995 to purify the film-making process. Dogma includes requirements that there be no background music and that films be shot with a hand-held camera, without special lighting or filters, which give them a shaky, documentary feel. Von Trier said he had no moral qualms about making the film. "I like the film to have different messages," he said. That's what art is about -- to portray any aspect of life. I have no moral problems with that."