"What [Courts] find is deemed to be the truth but this is a convenient legal fiction and it must be remembered that it is not always actually the truth. Parties will be more satisfied with the system if this is more widely acknowledged. We must not allow [Court] decisions to construct our reality."But constructing reality from court cases is exactly what we do.
Consider that person A commits a crime and person B gets convicted for that crime. It may well be that person A and person B are the same person; in that case the right person gets convicted, but just because person B gets convicted doesn't mean that he did it, it doesn't mean that he suddenly becomes person A.
Of these two people, one is fact the other is fiction: person A is real whereas person B is a fiction. Person A can become person B, a person who commits a crime can become a person convicted of that crime; but person B cannot become person A, a person convicted of the crime, if he didn't commit the crime, cannot become the person who committed the crime because he was convicted.
But don't take my word for it, here's a quote from Lord Neuberger speaking extra judicially,
"...it was Lord Wilberforce who famously observed that the traditional function of a common law judge was not to seek the truth. As he put it,"
"In a contest purely between one litigant and another . . . the task of the court is to do, and be seen to be doing, justice between the parties . . .. There is no higher or additional duty to ascertain some independent truth. It often happens, from the imperfection of evidence, or the withholding of it, sometimes by the party in whose favour it would tell if presented, that an adjudication has to be made which is not, and is known not to be, the whole truth of the matter: yet if the decision has been in accordance with the available evidence and with the law, justice will have been fairly done."So when you hear that a person has been convicted of crime it is not a certainty that they did it, just a mere probability. As for a value for that probability, we should be finding that out in the near future.