It's so misused most of the time. The clearest, correct example of it I've seen is a sign that says "No Parking from 10PM to 5AM". This is an exception to the otherwise unstated rule that parking is allowed during all other times, therefore proving it exists.
I disagree with most of the commenters that want to apply the phrase to heuristic claims.
This is currently the only reply that's downvoted below zero, but this is also the only reply that matches the definition of the phrase as I understood it.
I disagree with most of the commenters that want to apply the phrase to heuristic claims.