Why France?

On November 13th, 2015, more than one hundred people were murdered in Paris, France. The murderers appear to be dead. I don't know why they thought that attacking Paris was a good idea. As far as I can tell:
If you punch an American, he'll punch you back.
If you punch an Englishman, he'll go get his friends and they'll take turns punching you back.
If you punch a Frenchman, the entirety of France will show up at your house and punch you back.

If Germany tried twice to subjugate France in the twentieth century and failed, what makes these terrorist groups think that they can do it? Are they insane? Are they stupid? Both? This attack was so senseless as to be absurd, and the effect will be to unite France against whatever purpose these murderers claim to serve.