Craig Ferguson apparently thinks he has figured out why Conan O'Brien failed to succeed as Jay Leno's successor on The Tonight Show. "Look at the terrible thing that happened to Conan when Conan tried to do what Jay Leno does," Ferguson told Reuters on Monday. "Conan shouldn't do that. He doesn't do what Jay Leno does. Jay Leno does what Jay Leno does. And then when [Conan] started doing what Conan does, it was too late." As for himself, he insists he has no ambition to replace David Letterman when and if Letterman steps down. (Ferguson's late-night show is produced by Letterman's Worldwide Pants.) "The thing is, Dave's doing a great job and he does what he does. I don't do what David Letterman does," Ferguson said.