Nothing is being created. You're right, it is completely a gamble, unless you have some form of (not necessarily illegal) insider knowledge. But capitalists love the art of stock gambling because it gives the feeling that is related to something productive (a business). And they also perfected the art of extracting money from society (pension funds, retirements, sovereign funds) to fuel these stock-trading activities. So it is very lucrative for a small group, a little over inflation for many people, and a big loss for a lot of less fortunate investors. It also help concentrate business in the hand of a few, because if you have lots of money you can buy the advice of the best money managers and let the small investors bear the losses.