It might typically take 100 boycotters to ensure that one less crate of 100 steaks is bought. But one of those hundred individual choices must have made the difference between the store choosing to buy X crates or X-1. We just don't know which one -- where the tipping point lies -- whether we just need to decrease demand by 1 more steak, or 36, or 99, before the store will respond. So, in the absence of any further information, any individual consumer should see their personal steak boycott as having a 1/100 chance of reducing the store's purchasing by 100 steaks. (And so on up the supply chain.) That's an expected impact of (ta-da) one steak. The "chunkiness" of the market's sensitivity thus makes no difference. Your lessened chance of making an individual impact is exactly counterbalanced by the higher steaks payoff if you happen to succeed in influencing an entire 'chunk' of demand.
But verbal ingenuity aside, it does lead me to wonder at the kind of world which would lead one to think that almost all of one's day-to-day choices are, you know, inconsequential. Isn't it so like the sleek casings with which we like to have our electronics masked, to protect us from the complexity of their real mechanisms? You can scratch an iPod with a nail for hours without messing up its operation.
There's a reflection cooking somewhere in there on the connection between macroeconomics and the essence of technology. I just wanted to give you a whiff of it.