Have you ever thought that somebody suspected you of something, and as you offered a relevant explanation, you found yourself drifting into tangents and having to amend things that you’d just said and thought, “he’s going to think I’m lying”? Well, research suggests that what appears to be poor lying skills may be the natural expression of honesty:

Kevin Colwell, a psychologist at Southern Connecticut State University, has advised police departments, Pentagon officials and child protection workers, who need to check the veracity of conflicting accounts from parents and children. He says that people concocting a story prepare a script that is tight and lacking in detail.
“It’s like when your mom busted you as a kid, and you made really obvious mistakes,” Dr. Colwell said. “Well, now you’re working to avoid those.”
By contrast, people telling the truth have no script, and tend to recall more extraneous details and may even make mistakes. They are sloppier.