I think there is no definite answer, and it's therefore only natural that common insights contradict each other. I've read Ben Graham's often recommended book, and the take there is that the market is a lot of times completely irrational, if not most of the time. A reason for a stock going down could be that it's not "sexy" and not viewed as the future big thing, but if the company has a solid business model, people will come back to it. There were plenty of examples of that. But what is a good business? Well, you need to know a lot of metrics companies publish on their earnings, debt etc. and also you need experience to see through any possible accounting shenanigans (e.g. Under Armour admitted last year they kept moving future earnings to the current quarter so it seems their current quarter was more profitable than it really was).

The reality is that it's much more complicated than any one liner, and that most normal people that invest, invest based on gut feeling. It only really works by chance. Or they invest in index or mutual funds.