In his Courts on Trial, Jerome Frank suggested that procedural reform was a "necessary" but not a "sufficient" condition. "Aware that the ‘substantive’ rules, no matter how excellent, won’t work, and become futile, if the procedural rules are too rigid or otherwise seriously defective, some wise lawyers, the ‘procedural reformers,’" Frank argued, "have insisted that the procedural rules must be so revised as to provide efficient ‘machinery’ for the vindication of ‘substantive’ rights. These reformers, who at first glance seem to have escaped the thralldom of legal magic, have, in recent year, successfully achieved many of their reforms.

Yet, judged by their aims reformers have failed. For all their admirable efforts, they have not succeeded in bringing about what they promised - the easy, simple, unimpeded operation, in court, of the substantive rules in such a way as to prevent litigants from losing suits which, under those rules, they should win. Why?" Frank asked, "Because, having correctly concluded that improved procedure is necessary for the effective operation of the substantive rules, these reformers mistakenly thought that improved procedural rules, without more, would do the trick....

... the word ‘machinery’ is often used by these reformers to describe procedure. But well-working judicial machinery, while essential, is not alone enough to enable the courts to give full effect to substantive rights. These reformers, by creating the erroneous belief that well contrived substantive rules plus well-contrived procedural rule "machinery" will suffice to produce competent judicial administration of justice, have raised false hopes. They have themselves largely disregarded, and thereby unfortunately deflected attention from, the non-machinery elements of the decisional process. Even if we have the best judicial machinery, those non-machinery elements will often lead to decisions which balk the operation of the substantive rules.

For the products of a machine depend (1) on the material which goes into the machine [the failure of a litigant to obtain crucial evidence because he lacks funds to make a pre-trial investigation, or the mistakes (deliberate or inadvertent) of witnesses] and (2) on the persons who operate it [trial judges and juries]." [Jerome Frank, Courts on Trial; Myth and Reality in American Justice (1949), 103-105].