Instead, we should recognize that being "proven" is not a binary yes or no, but rather a sliding scale.

Or, to use Popper's model of falsifiability, we could say proven is a binary of no and maybe. Maybe is worth investigating and improving, no is no. If a charity cannot express how they know they have failed, I hesitate to trust they know they have succeeded. It can be a simple thing to express negation (if this soup kitchen does not give away X bowls of soup in Y period of time, we have failed and therefore Z) especially if the bar is set low, but I have never seen a charity do so.

My theory: People want to back the strong horse so they avoid charities that say they might not be 100% successful. Charities talk mostly of how the world fails a cause (therefore them) and not how they might fail. No exit strategy, too pure of heart to fail. This also explains mission creep in charities: if they succeed, they fail to have a reason to exist and so must now adopt cause P and Q as well as R, because (now) they are all connected. And perhaps a bit of self-importance / parent shaming: this agency / generation is going to end homelessness ('cuz you other / older guys were too mean or too dumb to do so).