Many Superfund practitioners have spent years litigating cases in which a private plaintiff seeks to establish that defendants are liable for costs of responding to a Superfund problem and that they ought to bear some specific equitable share of the total responsibility. Often, the plaintiff has brought the case even though the plaintiff has not paid a very significant portion of the total costs, has not committed to pay a significant portion of the costs, and has not been adjudicated responsible for anything. Why does that private plaintiff get to trigger allocation litigation?