Volenti non fit injuria

Volenti non fit injuria (Latin: "to a willing person, no injury is done") is a common law doctrine which means that if someone willingly places themselves in a position where harm might result, knowing that some degree of harm might result, they cannot then sue if harm does in fact happen. The 'volenti' only applies to the risk which a reasonable person would consider them as having assumed by their actions; thus a boxer consents to being hit, and to the injuries that might be expected from being hit, but is not a 'volenti' if (for example) his opponent should swing an iron bar at him, or punch him outside the usual terms of boxing.
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Latin: to one who is willing, no harm is done. - (read more on Volenti non fit injuria)