The eccentric 28-year-old revealed that he is "not a really confident actor" at the war movie's European premiere on Sunday, after recently admitting to suffering an "existential crisis" and making some "judgement errors".
"I don't have faith in my abilities," the US actor told the Guardian. "It's like if I told you to react to a gunshot right now. It would be much easier if I just got a gun out and pulled the trigger, because you wouldn't have to conjure anything. You would just react to it.
"I try to alter my life so that I don't have to conjure anything or to make believe."
LaBeouf also spoke about the tough "physical and psychological" boot camp set up for the Fury cast by producers.
"You get to 100 push-ups and they'd say 100 more, then when you do that it would be 100 more," he said. "You have to rely on each other because if I can't do it, Jon (Bernthal)'s got to do them and if he can't Mike (Pena)'s got to do them and so forth.
"You learn to relinquish yourself as the 'we' of it rather than the 'I'. It takes the selfishness away."
LaBeouf's co-star Logan Lerman confirmed that the cuts on his face were real in an interview with British GQ earlier this month.
"They were putting cuts on Shia and I said 'Yeah, yeah, it looks good'," he said. "But Shia was like 'No, it doesn't look real'. He walks out into the hallway and says, 'Hey man, wanna see something fun? Check this out…' and he takes out a knife and cuts his face."
Past reports have also suggested that LaBeouf, who plays soldier Boyd 'Bible' Swan in Fury, did not shower while filming and learned to operate the tank with expertise.
Lead actor Brad Pitt praised LaBeouf's "full on commitment" and named him as "one of the best actors" he has ever seen. Pitt stars as army sergeant Wardaddy, who takes a five-man crew on a life-threatening mission into the heart of Nazi Germany.
The film, described by LaBeouf as about "intimacy among men", reaches UK cinemas on 22 October.Reuse content