Olivia Munn could only enjoy her role in 'Iron Man 2' when Robert Downey Jr. complimented her.

The 29-year-old actress - who plays the socialite-turned-superhero Janet Van Dyne in the action movie - couldn't get excited about the part until she met her famous co-star who helped her to relax.

She said: "I should take a deep breath and go, 'That's pretty cool.' But I'm afraid to take any of it for granted. When I was with Robert Downey Jr. on set he was just so complimentary. I let myself be happy then."

The brunette beauty - who is best known for being the face of the US cable network G4 - also confessed she is so scared of failure in Hollywood she tries not to get too carried away by any successes she has.

Speaking of her reaction to getting the part in 'Iron Man 2', she told FHM magazine: "Jon Favreau, the director, had talked to me a bit about it. He said he'd love me to be in the movie. I get excited about things, but I don't freak out because I get afraid.

"I feel like if I put my head up I'll get hit by a bucket and it will be all gone, so I get to the point where when something good happens, I take it and I keep moving because it could all go in a minute."