Are you afraid? You should be. Very afraid. That's the absolute proof that terrorism is effective.
Terrorism isn't new*. It has been used effectively throughout history, usually against repressive governments. Gandi was a terrorist against Imperial UK. Ben Gurion was a terrorist, again, against Great Britain. Our Founding Fathers were considered traitors and terrorists by King George. Duke Ferdinand was assassinated by terrorists resulting in WWI. Lenin was a terrorist who eventually overthrew a repressive and ineffective tsar.
Terrorism, by definition, creates fear. It also enables the target government better control over its own population. Result: more control over the population in the name of security. All resources are diverted to protection against the terrorists, and the fearful population doesn't pay attention to increased government interference and control over their lives. The targeted government tends to continue to feed the fear with color-coded alerts and other measures.
Terrorism works.
*If you didn't study history in high school, you won't understand any of this. Too bad. You had an inferior education.