In his justly famous decision in The T.J. Hooper, 60 F.2d 737 (2d Cir. 1932), Judge Learned wrote that:
... in most cases reasonable prudence is in fact common prudence; but strictly it is never its measure; a whole calling may have unduly lagged in the adoption of new and available devices. It never may set its own tests, however persuasive be its usages. Courts must in the end say what is required; there are precautions so imperative that even their universal disregard will not excuse their omission.
In other words, in negligence cases, courts will usually defer to industry standards but in some cases courts will be prepared to say that a universal industry custom may be so deficient as to itself be negligent.
Contrast that approach to Delaware's consistent jurisprudence on corporate governance best practices. The invaluable Francis Pileggi draws to his readers' attention the latest case to hold that legal liability will not result from a failure to come up to best practice:
The best way to explain the noteworthiness, for those engaged in corporate litigation, of the recent Delaware Chancery decision in Wilkin v. Narachi, C.A. No. 12412-VCMR (Del. Ch. Feb. 28, 2018), is to quote from the Court’s introduction: “This case … is a prime example of the difference between a best practice and a legal obligation . . . but Plaintiff fails to point to a single legal obligation that directors violated … [and] Plaintiff has not pled facts that give the Court reason to doubt that these [unexpectedly less successful] outcomes stemmed from rational, good faith decisions of faithful, loyal directors.”
It seems there may be one of to things going on here. First, best practice may differ from "common prudence." On this issue, cf. Dan Laidman, When the Slander Is the Story: The Neutral Reportage Privilege in Theory and Practice, 17 UCLA Ent. L. Rev. 74, 104 (2010) ("While rare, it is not unheard of for courts to look to journalistic best practices in the same way that they use customs in other industries as proxies for reasonableness and negligence when determining tort liability."). But see Niva Elkin-Koren & Orit Fischman-Afori, Taking Users' Rights to the Next Level: A Pragmatist Approach to Fair Use, 33 Cardozo Arts & Ent. L.J. 1, 22 (2015) ("Rothman claims that such [fair use] Best Practices, at best, reflect wishful thinking and not the de-facto industry custom, and at worst, create reality but do not describe it").
Second, because negligence is not a relevant standard in Delaware corporate law--the duty of care is violated by gross negligence--perhaps industry practice is less relevant than tort law.
Interestingly, according to Westlaw, no Delaware court has ever cited The TJ Hooper.