Imagine, for a second, a doorman who behaves as automatic doors do. He does not acknowledge you when you approach or pass by. He gives no hint which door can or will open-until you wander within six feet of the door, whereupon he flings the door wide open. If you arrived after hours, you might stand in front of the doors for awhile before you realize that the doors are locked, because the doorman's blank stare gives no clue.
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