The purpose of terrorism is to provoke an overreaction

"The purpose of terrorism is to provoke an overreaction. Its real aim is not to kill the hundreds of people directly targeted but to sow fear in the rest of the population. Terrorism is an unusual military tactic in that it depends on the response of the onlookers. If we are not terrorized, then the attack didn't work. Alas, this one worked very well."

— Fareed Zakaria