When I was in college, I did a summer in a research lab doing something with mice. What, I don't remember. All I know is that by the end of the summer, my hands were covered in little mouse bites. Probably because when they were under anesthesia, I'd cuddle with them in my hands and not be vigilant enough of when they were waking up.
One of my coworkers was a 25 year old graduate student named Elaine. She got engaged that summer and was totally excited about it. At the time she seemed really old, but in retrospect, she seems really young.
Another of my coworkers was a 30-ish post-doc named John. (At the time he seemed really old, but in retrospect, he seems really young.) He was not super happy there, mostly for monetary reasons.
During that fateful summer, two things happened:
Elaine quit her grad program to get a job teaching science at a high school.
John quit his post-doc to get a job "in industry" that paid twice as much.
It never occurred to me that this was a little bit odd that two people quit a lab in one summer. I mean, maybe it isn't odd, I don't know. Maybe people quit grad school and post-docs all the time? The lab itself wasn't particularly horrible. The boss was pretty nice. I found it really boring working there, but I had no idea what I was doing.