Mostly it is the illusion of control, you don't have it, you only have choices you can make in the face of unfolding events. At Zach points out, companies change as they grow, they are some weird strange attractor function that emerges from the collective personality of everyone working there. When I joined Sun for example it was the coolest place I could ever imagine being, when I left it was a enterprise focused sales engine. Same company but different places.
I will say though that when I meet someone who has been fired or "let go" repeatedly from job after job, then it is a different situation entirely. Something I doubt Zach will experience.