The Behavior Design Blog on Medium covers habit formation, product psychology, and ethics of addictive technology, with posts on apps and startups.
HN links it for its habit and behavior posts; the one commenter quotes its toothbrush test, attributed to Larry Page, for judging companies.
From https://medium.com/behavior-design/the-toothbrush-trick-used-by-googles-ceo-to-get-customers-to-come-back-910d81c272b4:
> Larry Page, CEO of Alphabet (the company formerly known as Google), has a quirky way of deciding which companies he likes. It’s called “The Toothbrush Test.” According to the New York Times, when Page looks at a potential company to acquire, he wants to know if the product is, like a toothbrush, “something you will use once or twice a day.”