If Israel found an attack from Hamas at this point as hard to imagine as they claim to, why in the world would we expect civilians to be better informed.
Some people, obviously mistakenly, believed Hamas to have cooled down a little bit and to be genuinely interested in making the lives of civilians a little bit easier. The terrorist attacks of course illustrated forcefully that this was not the case, but it's hard to blame civilians for being surprised by this when Mossad apparently had no way of seeing it coming either.