Consider something as innocuous as the “notification” icon—the red dot that has haunted the Facebook app for a decade. No part of the design is an accident. Red is the color of agitation and psychological arousal, the mere glimpse of which can lead to a spike in heart rate. It feels good to make red things go away. Because notifications are purposefully vague until touched, following them can feel like opening a present. (Is the notification a long, heartfelt comment from a close friend, or just another forgotten acquaintance’s birthday?) While the notification icon was certainly intended to
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