When Argothian Wurm enters the battlefield, first the active player gets the option to sacrifice a land. If he or she declines, the next player in turn order gets the option. If a player elects to sacrifice a land, Argothian Wurm is put on top of its owner's library, but then all remaining players still get the option. If all players decline, then nothing happens and Argothian Wurm stays on the battlefield.