Swiss cheese, good that the theory was discovered on the 90´s but i´ve heard this since 40 years ago: an accident is the cumulus of different failures and are not always related to one individually.
I always like to read about airline accident so I can be more professional on my job and try to avoid them. Just remembered when I flew my first turboprop, the MU2-B, people told me that I was crazy, the japanese revenge!!!! I looked for all the info I could on the aircraft and found the problems for the accidents. 2 Years later I had one of those big problems, "Ice Acummulation", thanks I did my homework I could save my life and my co-pilot.