I think a lot about signal detection theory, and I think that's still the best I can come up with for this question. There are false positives, there are false negatives, they are both important to keep in mind, the cost of reducing one is an increase in the other, humans and human systems will always have both.

So, for example, even the most over-generous public welfare system will have deserving people off the dole and even the most stingy system will have undeserving recipients (by whatever definition), so the question (for a welfare system, say) isn't how do we prevent abuse, but how many abusers are we willing to tolerate for every 100 deserving recipients we reject? Also useful in lots of medical discussions, legal discussions, pop science discussions, etc.