The Achilles principle (that would be, 'time wounds all heels')
In this case (Weaver v. Celebration Station Properties, Inc. (S.D. Tex. Apr. 28, 2015), it was time go-karting that wounded plaintiff's heel, when her go-kart was hit by another driver's go-kart. But defendant was under no duty to warn the plaintiff, because
[Plaintiff Kerri] Weaver was aware of the obvious risks of contact or collision while riding a go-kart on a track with other go-karts traveling at approximately 18 to 20 miles per hour…. Celebration [Station Properties, Inc.] owed Weaver no duty to warn her of the open and obvious dangers of go-kart driving.
And, though Weaver also argued that Celebration should have "maintain[ed] a database and system for tracking 'bad apple' drivers who had previously been reckless and caused collisions or wrecks," the court notes that Weaver offered no evidence "supporting an inference that the driver who bumped her go-kart and caused her injuries was a 'bad apple' who could have been screened through such a system." Sounds right to me.