 Economic analysts of law disagree amongst themselves about the appropriate structure of rules to reach the market-ideal level of risk. Some advocate a rule of strict liability, according to which the person carrying out an activity is made to “internalize” all of its costs. A rational economic actor engaged is such activities who was forced to internalize is costs would be indifferent between paying the costs of avoiding the accident or paying the costs of the accident. They will therefore invest resources in avoidance costs up to the point at which doing so will reduce expected accident costs. Strict liability therefore will yield an optimal investment in safety. It would give potential injurers an incentive to find innovative ways to make their activities safer, particularly in a world in which most injuries are caused not by isolated acts but by ongoing activities such as the manufacture of consumer products or the operation of motor vehicles (Calabresi 1965).