I was part of a group people that tended towards artsy (and definitely not rationalist). This was when everyone had an idea for a new app, and I kept getting people trying to get me to work for equity. They seemed to have these same kinds of unrealistic expectations. I eventually came to the conclusion that they saw software as like painting. It seems to take about 8 - 24 hrs to create a work of art (assuming the idea is complete and you are working within your skill level), so their mental price and timeline was something similar.

A better metaphor for software is like writing a book. Everyone sees writing a book as borderline undoable, and the expectation is that it takes months and months. I think that software and writing have a lot in common (including lots of text, and even the verb used), and that explaining ourselves as book-writers would help set better expectations.