When is the optimal time for your employee to quit?

I found this great article on Hackernews - https://www.benkuhn.net/optopt. It's an oldie, but a goodie and still applicable today. Gives great insight for both employees and founders on how to structure and negotiate for the often misunderstood world of options! Also, provides insight on how to structure contracts to ensure your best employees are given incentive to stay after their vesting period.