If you show me a tool that does a thing perfectly 99% of the time, I will stop checking it eventually. Now let me ask you: How do you feel about the people who manage the security for your bank using that tool? And eventually overlooking a security exploit?

I agree that there are domains for which 90% good is very, very useful. But 99% isn't always better. In some limited domains, it's actually worse.

Counterpoint.

Humans don't get it right 100% or the time.