The problem is that people get complacent after long periods of quiet.
"Why are we wasting all these resources on a border that's clearly quiet?" "These damn war mongers in our government just want to increase the military budget to feed the industrial war complex!" "We are just intimidating those poor people."
...And so on.
Israel had the resources, they were caught off guard. A totally different kind of complacency to an underfunded and incapable military.