Actually, that’s the short version. Here’s the long one.
Any opinion, value, product or service that achieves critical mass in terms of popularity will therefor become true (or false), or valuable, or not valuable (you get the idea) REGARDLESS of its actual characteristics.
Thus, you have pet rocks, Twitter, and other social media, other fads, myths about learning and training.
This is a deceptively simple concept that affects much of our lives. It explains that from a distance, or with people we don’t know well (and we may not know many people well) everyone seems psychologically intact, or “normal”.