You keep using that word, probably, as if it's a quantifiable number by which a firm can and will make their business model upon in such a manner which they can bank on gains/losses to actually turn a profit which they can model precisely (hint: they don't actually do this, I've worked in a restaurant). Seriously, making cute micro-econ models isn't science, it's phrenology. If you want to construct something with known quantities with known and repeatable events in a model then I'll listen. If you're going to give me Friedman's plucking model then I'm going to just put my headphones and ignore anything you have to say.