It couldn't be that Kahnemann made a beginner's mistake and interpreted a ceiling effect in his outcome as a moderator. No, "conventional practice" dictated labelling the outcome variable happiness, rather than unhappiness.
Tenure is one hell of a drug.
https://www.pnas.org/doi/10.1073/pnas.2208661120
> This income threshold may represent the point beyond which the miseries that remain are not alleviated by high income. Heartbreak, bereavement, and clinical depression may be examples
except happiness is normally distributed and subject to many additive effects