R v O’Connor – (1995) 4 SCR 411 (McLachlin):

[193] The task before us on this appeal is to devise a test for the production of records held by third parties which preserves the right of an accused to a fair trial while respecting individual and public interest in privacy and the efficient administration of justice. The key to achieving this lies in recognition that the Canadian Charter of Rights and Freedoms guarantees not the fairest of all possible trials, but rather a trial which is fundamentally fair: R. v. Harrer, [1995] 3 S.C.R. 562. What constitutes a fair trial takes into account not only the perspective of the accused, but the practical limits of the system of justice and the lawful interests of others involved in the process, like complainants and the agencies which assist them in dealing with the trauma they may have suffered. Perfection in justice is as chimeric as perfection in any other social agency. What the law demands is not perfect justice, but fundamentally fair justice.

[194] Perfect justice in the eyes of the accused might suggest that an accused person should be shown every scintilla of information which might possibly be useful to his defence. From the accused’s perspective, the catalogue would include not only information touching on the events at issue, but anything that might conceivably be used in cross-examination to discredit or shake a Crown witness. When other perspectives are considered, however, the picture changes. The need for a system of justice which is workable, affordable and expeditious; the danger of diverting the jury from the true issues; and the privacy interests of those who find themselves caught up in the justice system — all these point to a more realistic standard of disclosure consistent with fundamental fairness. That, and nothing more, is what the law requires.