You'll hear some people point out that statistically, your individual chance of being killed in a terrorist attack is very small - less than your chance of being struck by lightning, or sucked up in a twister, or trampled by a caribou, or whatever.
And that's factually true, but it misses the real threat of terrorism, which is to gradually intimidate society and its institutions into complying with the objectives of the jihadi islamist movement behind the attacks.
By incrementally applying pressure, first here, then there, they hope to erode the resistance of a free society over a period of time. These guys aren't stupid. They are smart, sophisticated, and very very patient. They know what they're doing, and they know that it works.