How and where does retainers fit into the ff14 world/society?

[Minnel]

Are retainers just out-of-the-lore, convenience kind of deal or is there an actual lore for who and where they come from? Cause I vaguely remember doing the retainer quests as a sprout. Apparantly some 'owners'/customers are stingy and poorly equips their retainers, leading to retainers' death sometimes. Like damm. Either retainer is extremely well paying job or someone is holding a gun point to their head to do whatever customers ask of them. It's also interesting how our retainers can study a job into oblivion and become one of the 'advanced classes' if asked. I'm really interested to know how they choose retainers cause they seem like a group of extremely talented,and service-friendly, people.

P.S.: Sorry for horrible grammar