The Chazon Ish gave a parable. A general fought a battle to defend his country from an enemy from the north. When he died, his son assumed his position. Years later, the country again came under attack, this time by an enemy from the south. The son dispatched the army to the north, because his father had done so. He was reprimanded, "You fool! Your father sent the army to the north because that is where the attack from. This time it is from the south, and that is where the army must go."
The Chazon Ish said, "Every generation faces new threats. We must confront the current threats and not those of previous generations if they no longer exist."
Rabbi Abraham J. Twerski in Angels Don't Leave Footprints.