Question from someone that has never played with stocks: when someone like the writer or some random friend tells me that stock X is undervalued or overvalued,

Question from someone that has never played with stocks: when someone like the writer or some random friend tells me that stock X is undervalued or overvalued, do they really have any objective way to evaluate that? What do they think they know over other people that are willing to sell the stock to them? Over the past two years I have seen more and more friends starting to do day trading, some of them even waking up hours earlier before work to read about stocks and organize their trades for the day. Is this really just irrational gambling with extra steps? And if so, why aren’t those people, which I consider pretty reasonable otherwise, are led to believe their reasoning and knowledge will give them an edge.