Broadly speaking, it comes from the value they provide to other humans, aka a person's value to society. At this point in human history, career is generally a p

Broadly speaking, it comes from the value they provide to other humans, aka a person's value to society. At this point in human history, career is generally a proxy for this metric. E.g. doctors have high social value because they save other people's lives. Wealthy people have high social value because they have the potential to make those around them wealthier, etc. This value derives from the average person's lack of the things that the other people provide. Suppose AI could provide all those things. Once AI becomes self-maintaining, the only value that humans could provide each other would be entirely social.