[bombcar]

The problem “fiddle and see if Rome burns” is that you may have broken something that only runs once a year/decade and you won’t know if that process isn’t in the list of tests.

And by the time it breaks, will anyone remember the probable cause?

[wpietri]

If people are building things that only run once a year or once a decade and haven't included sufficient tests to make sure those things work and keep working, then the failure lies with them, not with the people who work on the system later. The real "probable cause" isn't some later change. It's the initial negligent construction.