The principle
Emotional states are contagious. Associate with the chronically miserable and you will absorb their misfortune; associate with the genuinely fortunate and the opposite occurs.
The application
This is the cruellest-sounding law and one of the truest. The rule is not "abandon the suffering" — it is "do not adopt the chronically self-defeated as your daily company." Compassion has limits; proximity has consequences.
The defensive tell — how to spot it being run on you
When someone in your circle reliably re-frames every opportunity as a threat, every win as a fluke, and every conflict as proof the world is rigged, you will eventually start narrating your own life the same way. Distance is the protection. Affection survives at distance; identity does not always survive proximity.