Great post. I think this is one of the fundamental lessons that all startups going through an incubator should learn: have a product, find a customer.

The most basic, lowest-common-denominator example of this is arbitrage. Buy one product for X and sell it for X + 10%. If you can't do that with one product successfully that you know there is already a market demand for (e.g. chairs) then how on earth are you going to do it for your startup?