My Empathy Theory, Part 1

One popular topic in the cognitive science community is empathy. There are many theories about why humans have empathy, and they generally involve special brain mechanisms such as mirror neurons. I've often felt that these theories are overly complex and that there should be a simpler explanation for empathy. 

I'm therefore happy to offer my own theory in which empathy emerges from a few simple rules and require no special circuitry at all.

I will present my theory in four steps:

1. Describe an everyday scenario involving two people, Bill and Sally, in which empathy occurs.
2. Explain (1) in terms of how a brain operates.
3. Suggest a different way of looking at what a mind is based on the results of (2).
4. Provide a set of associated theories/observations based on (3).

Here we go!