Retailers segment their customers' trips to the store in much the same way a tech company segments use cases. So-called "stock-up trips," typically conducted af

Retailers segment their customers' trips to the store in much the same way a tech company segments use cases. So-called "stock-up trips," typically conducted after the first payday of each month, are when customers go to the stores to -- as the name implies -- stock up on groceries and supplies for the coming two weeks. "Fill-in" trips are ad hoc trips to grab specific items or meet needs that have emerged since the stock-up trip. A second stock-up trip typically happens around the second payday of the month. And so forth. Shopping behavior -- particularly shopping behavior among segments of the population living paycheck to paycheck -- follows very predictable patterns like these, often by necessity. Now, let's put this into practice. I'm managing a regional grocery chain. Let's say it's Kroger in the Midwest. I want to win customers' share of wallet on the payday stock-up trip, so they'll go to my store instead of a competitor's (let's call that competitor Meijer). I'll time my sale accordingly on key items (often these are "price indicator" items that signal price superiority over other competitors in the area). Meijer will be timing its sale the same way, and so a lot of game theory and competitive intel will come into play here. But this is why grocery items and household necessities are cheaper at these big chains two weeks out of the month.