"We have no idea how this could have happened." That is the reaction Israeli officials have been giving today when I ask them how, with all its vast resources, Israeli intelligence did not see this attack coming.
Dozens of armed Palestinian gunmen were able to cross the heavily fortified border between Israel and the Gaza Strip, while thousands of rockets were fired from Gaza into Israel.
Or if they did, they failed to act on it. Israel has arguably the most extensive and well-funded intelligence services in the Middle East. It has informants and agents inside Palestinian militant groups, as well as in Lebanon, Syria and elsewhere.
Sometimes these have been done with drone strikes, after agents have placed a GPS tracker on an individual's car; sometimes in the past it has even used exploding mobile phones.
On the ground, along the tense border fence between Gaza and Israel there are cameras, ground-motion sensors and regular army patrols.
The barbed-wire topped fence is supposed to have been a "smart barrier" to prevent exactly the sort of infiltration that has taken place in this attack.