Why Did Amazon's Second Employee Leave After One Year of Options?

Paul Davis, Amazon's second employee, left after the first year of his options vested so he could be a stay-at-home parent in Seattle. There were five years of options. He waited until the first year vested, then left and walked away with 1 1/5 of the options he would have had by staying the whole time. He thinks he might have paid $70 for the shares, and there was no way of knowing what they were going to be worth.