Terrorists are formidable opponents in a World War that is being waged against Western Culture and are well organized and extremely dedicated to achieving their aims - which are very entwined with their "Jihadi" or Holy War view of the world than they are with any specific dispute about any specific region. They are not a bunch of disorganized buffoons struggling valiantly to redeem their homeland.
Terrorists have no red lines in achieving these goals. They will attack anything using anything. The idea that this or that is inconceivable is not part of their thought processes.
Terrorists are careful planners: right now, potential targets are being investigated right here in the USA, and all of Law Enforcement knows this. Look at every potential target in your area like a terrorist might.
Nothing succeeds for a Terrorist like Success. Terrorists interpret any withdrawal, concession, or sign of weakness as a strong Go signal. This was seen back in Lebanon in the 80's after the first VBIED caused the US to withdraw from the region. Instead, the weapon of suicide terror became viable and has grown in use until today. It was seen again when Israel withdrew from its security zone in Southern Lebanon.
Terrorists are flexible and like any guerilla fighters are more capable of responding to change than any standing force. The modus operandi or the profile of yesterday can easily be changed for today. We have to look for the bomber and not the bomb. Focusing on yesterday's weapon is not only useless it is really dangerous.
Terrorists have a different concept of time than we do in the West. Their time scale is vast and they see things in terms of their History. It took 200 years to dislodge the Crusaders from the Middle East in the Middle Ages and so the current struggle is in its infancy from their point of view. They are patient. They can wait.
One of Islam's successful strategies against its opponents in Jihad has always been to lull the opponent into a false sense of security. This was done during the big Islamic Conquests of the 8th Century through the creation of treaties that were drawn up as part of a War strategy and revoked whenever it was felt to be the right moment. The Terrorist that sees security efforts dropping because people believe this is something that will happen to someone else is then ready to strike.
Force has always played a very critical role in the Middle East. The most successful Israeli leaders have been those that have understood this. The least successful were those that thought they could negotiate. Force is a language that the terrorist understands; it is his natural language.