There are some measures, like TSA in America, that appear to be more focused around the illusion of security than actually preventing acts of terrorism. But what about some of the surveillance efforts conducted by intelligence organizations within the Five Eyes?
Maybe this merely a display of my own ignorance, but I don't understand why the efficacy of surveillance measures (both domestic and non-domestic) isn't discussed more often. If governments were more open about all the terrorist attacks they were able to prevent ahead of time, maybe the general public wouldn't have such a negative opinion of them when one terrorist slips through the cracks.
This paper (https://www.cepol.europa.eu/sites/default/files/26-reinhard-...) has some interesting insights into the matter. While admittedly a slightly biased source, this ProPublica article also has some interesting things to say about mass surveillance (https://www.propublica.org/article/whats-the-evidence-mass-s...)