Cuban is referring to when Wall Street aggregates investors' money and gives it to growing companies. Trying to grow by "producing more than you consume and saving the difference" is called reinvesting the cash flow, aka bootstrapping in the startup world. But sometimes companies see a growth opportunity that takes more capital than they can get through cash flow which is when they turn to investors. In Silicon Valley they turn to VCs, but Wall Street is the only place companies can turn to raise the really big money up to billions of dollars.