In practice, you're not just betting on a random walk, you're also reading the news and thinking about the company's outlook, its thesis, and its public sentime

In practice, you're not just betting on a random walk, you're also reading the news and thinking about the company's outlook, its thesis, and its public sentiment. You also have other indicators like volume, and fundamentals such as earnings. There's day trading and longer time horizon investing. As you can see, it's a bit easier to do the latter instead :)