The OP is talking about bugs not complex system failures. These are not the same thing. It might take multiple bugs to cause a complex system to fail, because c

The OP is talking about bugs not complex system failures. These are not the same thing. It might take multiple bugs to cause a complex system to fail, because complex systems often have enormous amounts of complexity built in, but a single bug is often a fairly unidimensional thing. You can identify the root cause of a bug.