If I wanted to sell my half of the Discovery Café, either to Joe Partner or to someone else, then the price of my share of the company would depend on how profitable the Discovery Café is expected to be.

In order to determine the value of the Discovery Café I would need to look at the books to see how valuable the assets of the company are (Book Value), how much money the company earns (earnings), and how much of those earnings come to me (earnings per share). In all of this there are two very important aspects of valuing this company that most people forget.

1. I am using information from the past to make educated guesses about what will happen in the future. You can't just graph all the past data and draw a straight line though it. A lot will depend on how I evaluate the company's ability to grow and change over an uncertain future.
2. Price really is irrelevant unless someone wants to buy or sell.