Something already got wrong in your logic chain if you came up with something like “well maybe if I need to kill 1001 citizens the terrorist is hiding behind in order to save my 1000 citizens, maybe better not do anything and let him kill my citizens”.
Immediacy is simple in this case. We all know that if Palestinians do not attack Israel then Israel will not attack Palestinians. And we all know that no matter what, Palestinians are going to continue their unprovoked attacks. This means whoever comes up with “let’s attack first because otherwise we’ll get attacked” must be Palestinian, and a lying one.