During the 1982 Falkland Islands conflict, the British Royal Navy felt that its ships were safe from attack because of a sophisticated defense system that identified enemy missiles and shot them down. Attack after attack was repelled with no damage to a British ship.
Then the unexpected happened. The 3,500-ton destroyer HMS Sheffield was sunk by a single missile fired from an Argentine fighter jet. Later, an investigation revealed that the Sheffield's defenses did pick up the incoming missile, correctly identifying it as a French-made Exocet. But the computer was programmed to ignore Exocets as friendly. So the ship was sunk by a missile it saw coming and could have destroyed.
Men and women who want to be sexually pure in our impure society are like battleships floating on the open sea. A constant bombardment of sensual missiles is fired our way every day. If our defense system allows missiles we should avoid to penetrate our mind, we're in big trouble.