But how to prove your particular nudge really worked? I'm reminded of Malcolm Gladwell's The Tipping Point - ok, yes, maybe a bunch of kids in New York started

But how to prove your particular nudge really worked? I'm reminded of Malcolm Gladwell's The Tipping Point - ok, yes, maybe a bunch of kids in New York started a Hush Puppy revival, but a million other fads didn't take off, so if you try to study it you're just studying survivorship bias. Or maybe coincidence.