Actually a lot of people believe they are a random distribution. There is a great book "A Random Walk Down Wallstreet" which explains it.
The basic idea is the market is efficient (the Efficient Market Theory) and all information about the stock is alreay priced into the stock. Picking a stock to beat the market average is basically a random chance.
Sure, across all investments. Pro-tip don't invest in all investments.
Real life markets are very clearly not perfectly efficient. Nor is stock price a perfect reflection of available information. Many/most/all? stock is prices on expectation i.e. guesses, not facts. Then there are all sorts of shenanigans like astroturfing and illegal manipulations/trading.
The basic idea is the market is efficient (the Efficient Market Theory) and all information about the stock is alreay priced into the stock. Picking a stock to beat the market average is basically a random chance.