This is a classic example of correlation ≠ causation; it's quite possible that people with already-high wellbeing are more inclined to greet their neighbors (as

This is a classic example of correlation ≠ causation; it's quite possible that people with already-high wellbeing are more inclined to greet their neighbors (as well as the opposite of people with low wellbeing not being inclined to greet their neighbors). Whether forcing yourself to greet six neighbors every day actually "maximizes wellbeing" is unsupported by the presented evidence. That said, I wouldn't be too surprised if there was a causative relationship, especially with some of the more specific "social" and "community" wellbeing. Seems like a reasonable guess, and it'd be straightforward to test: evaluate wellbeing scores from before and after one starts making it a point to greet six neighbors per day.