I am constantly confronted by students, reliability engineers and other people banging fists on tables and saying …
… 89 percent of failures are random …
Firstly, 100 percent of failures are random. It’s just that there are lots of textbooks and experts telling us that a ‘random’ failure is one that happens irrespective of age. That is, a failure with a constant ‘failure rate’ where the item in question doesn’t appear to age or wear out.