Markdown as a pricing modality is ubiquitous in retail whereas everyday low price (EDLP) remains relatively rare (despite its several advantages, such as simplicity). This paper explores whether and why retailers can use either of these pricing modalities as an effective defense against a competitor entering the market with the alternative pricing modality. Various studies have shown that consumers are strategic and heterogeneous in their valuation of a product. Consumers are also shown to be regret-prone, and anticipation of regret affects their purchase decisions. Consumers experience availability regret when they are unable to purchase products due to stockouts and high-price regret when they miss an opportunity to purchase products at low prices. Considering such factors, consumers decide whether, when, and from which retailer to purchase the product. In such a market environment, we find that the possible entry of a competitor should deter retailers from using the EDLP pricing modality but not markdown. We also identify a new reason for the markdown retailer to ration stock (in addition to the reason for discouraging consumers to wait for the markdown). In particular, we show that the markdown retailer can use inventory rationing to preclude a cutthroat competition and bankruptcy after the entry of an EDLP retailer. We also quantify how consumer regret affects both retailers' decisions and resulting profits. In particular, in a competitive market, the EDLP retailer cannot simply disregard consumers' availability and high-price regret (even when it stocks ample inventory and does not discount prices). We show that high-price regret and availability regret have complementary effects on the markdown retailer's rationing strategy and the EDLP retailer's price decision. Finally, using a proprietary price data set from a large department store, we show that ignoring regret factors causes the markdown retailer to leave up to 20% of its profits on the table. In addition, in a competitive market, the markdown retailer rations too aggressively when regret is ignored and, as a result, leaves some of the forgone profit to its competitor-the EDLP retailer. The retail industry is often characterized by its slim profit margins. In such an environment, the aforementioned results also suggest that retailers should seriously consider investing in developing the capacity to estimate and quantify the role of regret in consumers' purchase decisions.