The temporary nature of life's shifting episodes is never more on display than in school and at work. In school I was almost always the new kid, making sudden exits and entrances from K to 12 across the Rust Belt. This experience has carried forth into my adult life, where I often feel like the new guy at work years after I've started. Of course, thanks to the attrition of the recent recession, that's literally been the case with no new hires in my wake.
But generally at the office, people are hired, let go and sometimes stay longer than you do. In a big organization it's all multiplied, and the faces often change more frequently than you can follow. You may share only one conversation with someone before he or she is gone and not even know his or her name. And when you realize the absence, you're left grasping at a ghost. ("The loud-breathing guy with the smoke-colored bifocals must've been shitcanned. I don't see him anymore. I miss that guy.")