How did Israel not know?

As the war in the Middle East unfolds in the wake of the unprecedented surprise attack on Israel by Hamas militants, one question comes up again and again: How did Israeli intelligence – and the intelligence of its Western allies – have no idea this was happening? Some of them, which in many cases take the form of other unanswered questions:

• in CNNJoshua Berlinger provides historical context: “It has been more than 17 years since an Israeli soldier was captured as a prisoner of war in an attack on Israeli territory. Israel has not seen this kind of infiltration of military bases, towns and kibbutzim since.” City-to-city fighting in 1948 War of Independence. How could a terrorist group from one of the poorest regions in the world be able to launch such a devastating attack?
• in POLITICO, Jimmy Dettmer cites reports that more than 2,200 rockets were fired at Israel from Gaza during the first hours of the attack; Planning is thought to have taken months or even years. “Hamas would have used its vast network of tunnels linking the Strip to Egypt, but how did it smuggle in the materials needed for such a massive attack without Israel picking up the traffic? And how did Israeli intelligence fail to notice that Hamas was ‘assembling thousands of home-made Qassam rockets?’