The initial 4 year schedule is largely irrelevant, considering high performers get large refreshers.
There's a lot of jumping around at the 3-year mark, especially for people who want to cash in their FAANG brand for a similar package somewhere else. But once you get to E5 and higher there is significant financial incentive to stay with FB for longer than the initial four years.
That’s a pretty big drop. It’s less if you have higher ratings or promo of course.
initial grant / 4 + (refreshers x 3) per year
to:
refreshers x 4 per year
in addition, refreshers are given at the current stock price whereas the initial was grant was given at the 4 years ago price which was much lower therefore appreciated considerably