> And those rapid responses would in turn trigger another round of email, and another. This reminds me of an effect of specials at a supermarket: it's not just

> And those rapid responses would in turn trigger another round of email, and another. This reminds me of an effect of specials at a supermarket: it's not just that people will buy more, to stock up; nor that it becomes affordable to more people (price elasticity); nor that new people will try it - but that if you have more, you will use more. Like more roads create more traffic. This is partly personal price elasticity, in that when something is cheaper, you can start using it in more ways - as a substitute for more expensive (or, if you have previously found substitutes for it, because it was too expensive; now you can stop substituting). But this is a change in behaviour which persists into the future (familiarity/habit), bumping up your consumption a notch. A quick email response is like a special at a supermarket. It's so cheap, you use more. Not responding is like a price increase - sales drop off.