It drives rigorous scientists crazy when forensic experts go into court and testify that some bit of evidence – fingerprints, carpet fibers, ballistics marks on bullet casings, etc. – is a "certain" match for the defendant or his gun. These are all examples of "pattern matching," and in pattern matching there is no such thing as a certain match. If you have a big enough data set and a clear enough print, you may get the chance of being wrong down to one in a billion, but you can never make it go away. So when senior scientists are asked to comment on forensic procedures, they always say that we need to quit the certainty talk and instead offer probabilities based on real statistical studies.
The problem with this is juries. Studies of mock juries have shown that if a fingerprint expert describes the print at the crime scene as a "match" to the defendant, jurors take this very seriously. But if the expert admits to any chance that the print might have come from someone else, even a 1 in 100,000 chance, jurors ignore his testimony altogether.