Originally Posted by lolwut

Nope the top of a regional airline seniority list collects substandard pilots over time. Say a class of 10 newhires is hired and the best 9 of them are able to move on to something better, only the bottom 1 remains. That bottom 1 continues to move up the list as the "best 9" from other newhire classes also leaves. Over time these "bottom 1"s who can't move on to anywhere better end up collecting at the top. This results in the bottom of the list having roughly 10% substandard pilots and the top of the list heading towards 100% substandard pilots.

This is where the term "lifer" comes from.