. . . self-assured witnesses who make a mistake - even on issues of little importance - undermine their credibility by raising doubts about their competency, their ability to judge their own abilities and their motivations.The cocky, arrogant, or over-confident witness builds a wall between themselves and the jury. Since normal, ordinary, and reasonable people know we all make mistakes, the over-confident witness projects an air of superiority which juries tend to resent. Consequently, when the witness is caught in a mistake the jury is quite happy to punish him by greatly devaluing his credibility.
"People giving testimony, or advice, or opinions should therefore be careful to express appropriate degrees of confidence in their assertions," the researchers write in a summary of their report in the January issue of the journal Psychological Science.
[The researchers] said the team's findings challenge the frequent tendency of attorneys to pressure their witnesses to project a strong sense of confidence and to minimize the use of hedges like "I think" or "maybe." Academic experts encounter similar pressures when asked to testify before policy makers, he said. But this first-of-its-kind study shows that such a strategy can backfire if a cocky witness gets caught in a mistake.
The over-confident witness is often one testifying as an expert, but the problem also affects the lay witness. The experienced defense lawyer preparing these witnesses for court will recognize the problem and take appropriate steps to temper their over-confidence.