*For All* thinkers look for the general rule and then search for exceptions. *There Exists* thinkers look for one special case after another until they have found them all.This deal-with-one-case-at-a-time philosophy shows up everywhere in the agile approach to software development. We design systems one story at a time. We write code one test at a time.
Agile thinking is *There Exists* thinking.
"For Exists" also eases communication. It's easier to agree on a story/feature to work as expected using a specific acceptance test instead of argueing about general rules and how the software is expected to behave.
Of course, the "...until they have found them all" is the hard part. However, if you haven't found them all, you still have a lot of confidence about the cases you already found.
Back to working on speeding up our acceptance tests :-)