Since the Founding, the doctrine of standing has assured that the federal courts "decide only the rights of individuals," Marbury v. Madison, 5 U.S. (1 Cranch) 137, 170 (1803), avoid hypotheticals, and refrain from issuing advisory opinions. A formidable guardian of separation of powers, standing confines the Article III branch to exercising the judicial power alone, while concomitantly prohibiting any incursions into the realms of the Legislative and Executive Branches.