I believe the tax law says that when you exercise the options, you owe tax based on the current market value of the shares versus your exercise price, even if you did NOT sell them. That's a pretty big tax liability so maybe he will sell some shares to offset the tax bill. The good part of the tax law is once the tax is paid, you do not pay taxes again regardless of what price you sold your shares. So when he eventually sells the shares much higher it's a real home run!