Making money by timing the market, like all gambling, is a zero sum game. Anything you win is coming straight from someone else's loss. Whenever it seems like the whole market is up, that's just paper earnings. You can't cash out without someone else buying in, so there's no way for the entire market to be winning at the same time. Just can't happen. (And let's not bring up the vig ... excuse me, the fees.)

When GM sells a car -- let's pretend we're talking about a time when that was happening profitably -- GM gets the money from the sale, the buyer gets a car, the workers get paychecks, the stockholder get a share of the profits. Everyone wins.

When your business model is timing stock fluctuations, you can win or lose regardless of how many cars GM sells. Workers are laid off, potential customers don't have new cars, there's no dividend, but hey, you shorted the stock, so you still made money. Someone else lost, though. It's less than zero sum.