[A]lmost all (92%) of the catastrophic system failures are the result of incorrect handling

[A]lmost all (92%) of the catastrophic system failures are the result of incorrect handling of non-fatal errors explicitly signaled in software.

Check out the postmortems linked in the references.
http://neverworkintheory.org/2014/10/08/simple-testing-can-prevent-most-critical-failures.html