One of the adaptive abilities developed by higher forms of life, especially in humans, is the ability to learn from our environment. At the most basic level we learn an association between 2 events (such as in classic conditioning). Many animals can do that. We humans, as we grow, also develop the ability to discern causality, in that we are able to distinguish, given 2 associated events, between cause an effect.
Apparently the Palestinians, stuck in their collective psychopathology, lack this skill.
The recent justifications by the Palestinians for the continued Qassam rocket fire at Sderot illustrates this. This reminds me of a maladjusted child, who misbehaves and is punished for his actions, and who then protests and misbehaves even more, claiming that he misbehaved only because of the actions of those around him who are only responding to his offensive behavior. The Palestinians, like the child, confuse cause and effect (or pretends to). Everybody knows (except the Pals themselves) that if the Palestinians were not perpetrating terrorist actions from Gaza, there would be no need for the legitimate security measures that Israel is taking, such as the closures, etc. Further reinforcing this pathology is the international community which refers to the "cycle of violence", thus absolving the Palestinians from responsibility.
Another explanation is that the Palestinians know very well the cause and effect, that the Kassams have nothing to do with Israel's behavior but more to do with internal Palestinian power struggles.
Probably the truth lies in a combination of the two.