In Siegel, the telegram was negligently sent to New York instead of Washington, D. C., where the plaintiff's friend was residing in a hotel.  The friend was going to take the money to Maryland, where it was legal to bet on horses.  As Posner notes, the court holds that Western Union had no notice of the potential loss.  Put aside the question of notice and ask who was in the best position to avoid the loss.  Western Union is a plausible answer; it was Western Union that negligently misdirected the telegram.  On this point, compare the following cases Posner also cites:  Kerr S.S. Co. v. Radio Corp. of America; Postal Tel. Cable Co. v. Lathrop; Providence-Washington Ins. Co. v. Western Union Tel. Co..