During negotiations with a startup once, when I asked about the number of shares outstanding (and, thus, what percentage I was being offered), they told me: "Don't think about it that way..."

But: that's the only way I can imagine thinking about it.

I was being offered, say, 0.1% of the firm. If it ends up being valued at $100M at acquisition, that means my stake is worth $100K. Assuming we go public and it's a $500M valuation, my stake would be worth ~$500K (assuming no dilution, which probably isn't realistic).

I can see why they didn't want me to look at it that way. They were asking me to take a pretty large reduction in my annual compensation because of the equity...unfortunately, the equity they were offering me wasn't going to be very valuable even in the optimistic case (and that's ignoring the substantial risk that the equity could also end up being worth nothing, or considerably less).