For example, New York Pattern Jury Instruction 1:22, entitled "Falsus in Uno", reads:
If you find that any witness has wilfully testified falsely as to any material fact, that is as to an important matter, the law permits you to disregard completely the entire testimony of that witness upon the principle that one who testifies falsely about one material fact is likely to testify falsely about everything. You are not required, however, to consider such a witness as totally "unbelievable." You may accept so much of his or her testimony as you deem true and disregard what you feel is false. By the processes which I have just described to you, you, as the sole judges of the facts, decide which of the witnesses you will believe, what portion of their testimony you accept and what weight you will give to it.One federal court has described the principle as "a hoary maxim which allows a fact-finder to disbelieve a witness's entire testimony if the witness makes a material and conscious falsehood in one aspect of his testimony. [citation omitted.] The maxim is based on the logic that a person may mistakenly testify wrongly and still be believable, but if a person testifies falsely, willfully, and materially on one matter, then his 'oath' or word is not 'worth anything' and he is likely to be lying in other respects." Enying Li v. Holder, 738 F. 3d 1160 (9th Cir. 2013).
Insurance companies' special investigators likely have a special appreciation of this maxim, as their jobs often involve determining whether an misstatement or inconsistency is a lie, whether a lie is material, and whether a material lie supports a denial of coverage based on its voiding of coverage. Not everything that is false is a lie, and not everything that is a lie voids coverage.
Coupled with the maxim mendacem memorem esse oportet ("a liar needs a good memory"), the falsus in uno, falsus in omnibus principle is something that special investigators (and attorneys) may and should keep in mind in assessing the credibility -- or more accurately, predicting how the triers-of-fact may assess the credibility -- of the insured or claimant.
In application, the principle can net a prevaricating insured or claimant zero. Like in this case. Be guided accordingly.