Earlier quoted context omitted.
It's a standard share trade strategy. The net cost is 0 - cash in = cash out. And taxation is zero because your profit is (at the time) 0. It also means you can do something else with your original investment. If it goes up 100x - cash out whenever. If it goes down to 0 - you have lost nothing at all apart from some time.
why is your profit 0? you buy 2 at $5k it goes up to 10k and sell 1. profit is current value - cost basis 10k - 5k = 5k profit that will be taxed
Because the 5k in the market is not a realized gain