homeI have been indexing over half my life. I think I was born with the mentality for it, though I'm sure nature-nurture arguments can be (and probably have been) made over whether it is innate or learned.
The indexing mentality is predisposed to visualize and articulate a web of connections, and enjoys categorizing and constructing a visual analysis of a unit of writing.
A little OCD is not out of place.
Some people have noted a propensity to enjoy and perform music among those who also enjoy and perform indexing.
The indexing mentality pores for long hours over text and achieves distinct euphoria when concepts begin to fall into place, when the web of connections emerges in a new piece of writing--the index, reflecting and providing access to the inner workings of the indexed text.
Much more could be said, many more links could expand on it...