[Swizec]

Engineering is about tradeoffs. How many once-in-a-thousand bugs do you fix before you tackle the one-in-a-million? Or one in a billion? What about if it takes $10/bug to fix every 1:1000 bug and $100,000 to fix one 1:1000000 bug?

Correctness is great in theory, but in practice it's a matter of what's important.

[mannykannot]

If you are only looking at probability and cost-to-fix you are overlooking something important - the cost if/when it happens.

[verdax_1]

This is really emphasized in things like dmfea and other failure mode analysis documents or regulated industry. They want you to document the likelihood, your ability to recover from the failure, as well as the cost o the failure. You can say that you didn't want to pay for someone fixing some unlikely fail mode but that's small consultation to the people whose lives your product is ruining.