And so it is: some more price-sensitive people will wait for the sale and buy a whole lot to last them to the next sale, while others don't care and just buy every week regardless. So you've managed to sell the exact same product at two different prices, using the "small hurdle" method I described before (forcing buyers to plan their coffee capsule purchasing).

Granted, this is not exactly at the "same time", but for a consumable product like coffee, sales aren't measured in such short scales anyway. They're still two effective parallel prices if you measure by quarter.