Jennifer Thompson can vouch for that. In 1984, as she was being raped at knifepoint, she forced herself to study and note "every single detail on the rapist's face" so she would be able to identify him.
At the police station a few days later, Thompson found her attacker in a gallery of photos. She picked him again out of a physical lineup. She took the stand in court to point him out, and he was convicted.
But 11 years later, DNA evidence pointed to someone else. "The man I had identified so emphatically on so many occasions was absolutely innocent," she wrote later.
Thompson had many minutes to get a closeup view. Often, arrests are made on the basis of brief glimpses, sometimes in dim light or at a far remove. But even in these instances, eyewitness testimony can obliterate other evidence, as well as common sense.
In 1990, a jury convicted David Dowaliby of suburban Chicago of killing his 7-year-old daughter, largely on the basis of a witness who, on the night of the murder, saw someone in a parking lot where the body was later found.
He was 75 yards away, the lighting "wasn't that great," and the witness wasn't sure if the person was male or female, or black or white. All he knew was that the "nose structure" matched Dowaliby's. A jury voted to convict. It took an appeals court to throw out the case.
But many times, mistakes go undetected and uncorrected. We all know it's dangerous to believe everything we hear. The criminal justice system ought to acknowledge that the same holds for what we see.