Only when they are sold, or if you receive dividends. If he doesn't sell them he doesn't pay tax on them. He can then leverage those stocks BTW to receive loan

Only when they are sold, or if you receive dividends. If he doesn't sell them he doesn't pay tax on them. He can then leverage those stocks BTW to receive loans, which he won't pay taxes on as they are a debt. Then he can make use of the stock without selling it, and then use that extra income to invest in other things that will generate him additional income/capital or whatever. There are even more tricks you can do at that point, where on paper you are technically making a loss and never pay a cent in tax.