How long does a gearbox last?

I'm curious to know, how long can we expect a gearbox to last under normal operating conditions? Is there a specific lifespan or does it vary based on factors like usage, maintenance, and the quality of the gearbox itself? Are there any common issues or wear-and-tear points that typically lead to a gearbox's failure, and how can we prevent these from occurring to extend its lifespan? I'd appreciate any insights or recommendations you might have on maximizing the longevity of a gearbox.