O'Sullivan v. Shaw 431 Mass. 201, 726 N.E.2d 951 (2000) O'Sullivan was swimming in Shaw's pool. He attempted to dive head first into the shallow end and was injured. He sued Shaw for negligence. The pool was not marked, but O'Sullivan testified that he knew he was diving into the shallow end and knew he could be injured if he hit his head on the bottom. The Trial Court granted summary judgment to Shaw and dismissed the case. O'Sullivan appealed. The Trial Court found that diving into the shallow end is an "open and obvious danger" which was known to O'Sullivan. Therefore Shaw did not owe O'Sullivan a duty of care. The Appellate Court affirmed. The Appellate Court found that landowners are relieved of the duty to warn of open and obvious dangers on their premises because it is not reasonably foreseeable that a visitor exercising reasonable care for their safety would suffer injury from such blatant hazards. If the person was so dumb to hurt themselves on an obvious danger, then a warning from the landowner not to do it would probably not affect their decision. O'Sullivan unsuccessfully argued that the Trial Court had essentially allowed Shaw to use the defense of assumption of risk, which was abolished by the concept of comparative negligence. So instead of foreclosing all possibility of damages, the jury should instead to decide what percentage of the fault was O'Sullivan's and what percentage was Shaw's. However, the Court ruled that comparative negligence is only appropriate when the plaintiff voluntarily exposes themselves to a known danger caused by the defendant's negligence. This case was not a matter of contributory negligence or assumed risk, it was instead a no duty rule. Since no harm was foreseeable, then there is no duty to warn.