For no reason in particular, I was reminded of this Russian saying; to my surprise, it seems to have had little exposure in America, so I thought I'd do my part.

As I understand it, the word "lies" is understood to be something of an overstatement: The suggestion is simply that eyewitnesses are often mistaken about important matters, and perhaps also that they nonetheless overstate their confidence in their accuracy (since after all they saw the event with their own eyes).