Most of us figure negativity only hurts when it's aimed at us. Research says being nearby is enough. In one set of experiments, people watched a stranger get snapped at for showing up late. Afterward they solved fewer puzzles and were less willing to help anyone. Nobody had said a word to them, and just being in the room did the damage. It gets physical too. Ohio State had married couples argue for half an hour, and the ones who were hostile as a habit healed small wounds at about 60 percent the speed of kinder couples, with more inflammation in their blood. Facebook actually tested this at scale. For one week they quietly adjusted what almost 700,000 people saw. Cut the positive posts from someone's feed and they got more negative. Cut the negative posts and they got more positive. None of them knew. Mood spreads in both directions, which means you're shaping somebody's environment every time you open your mouth or hit post. Be picky about what you soak in all day. And be the Npub people feel better after scrolling past.