Even they can be caught out. There's a huge difference in someone whose mind is so addled--and a liar.
A liar will have his/her answer in a nano-second whereas a person whose mind is otherwise distracted, won't.
Unfortunately, Lookout, despite your need to cling to your firmly held beliefs. Liars are no more guaranteed to produce an "answer in a nano second" than psychopaths are guaranteed to commit murders. For both, though, the important thing is that they appear to be -and make a convincing act of- credible and sincere.