I don't think it's a hard rule; it seems to apply to certain companies who pursue a strategy of deliberately not making any money at first and just acquiring as

I don't think it's a hard rule; it seems to apply to certain companies who pursue a strategy of deliberately not making any money at first and just acquiring as many users as possible to reach critical mass and ward off competition, and then after-the-fact slap on monetization practices (specifically Ads) that degrade the product and piss off users. People don't like it when you mess with their products, especially once they already have something they really like. It's all about expectations.