Between the networking, the interviewing, the negotiating, and the onboarding, moving on or up can feel like a job of its own.

In 2009, two US professors set out to study zookeepers and aquarium workers in an effort to discover what kept them motivated at work.

The results pointed to an overwhelming similarity: The keepers gained a deep sense of meaning from their jobs. It didn’t matter that caring for animals was extremely badly paid and offered little career advancement, or that many of the actual tasks involved could be classified as “dirty work”—cleaning up feces, chopping vegetables, scrubbing floors. The zookeepers, most of whom were highly educated, felt that they were fulfilling a calling, and in doing so were extremely dedicated, often volunteering for months before even beginning to be paid, and rarely quitting.

“I can’t think what would cause me to leave” was a common sentiment noted by the researchers, who surveyed almost 1,000 zookeepers, and conducted in-depth interviews with many of them. But the fact that the keepers had found and followed a calling was a double-edged sword. Doing what they did for love also meant putting up with poor conditions and potentially being exploited.