How many water bottles does any one person need? For some people, need isn’t the issue. It’s about buying things they say make them feel good, and showing them off online.⁠ ⁠ The Stanley Quencher tumblers—which currently retail for $45 for the 40-ounce version, or $50 for limited releases—have ignited tussles at Target stores and become a viral topic online. They are the most recent example of a shopping trend: buying multiples, and sometimes dozens, of the same item.⁠ ⁠ Thank, or blame, social media, where users flaunt their collections, showing off shelves lined with water bottles on TikTok and Instagram. On TikTok, the hashtag #stanleytumbler has 1.2 billion views and more than 67,000 posts, the social-media platform says.⁠ ⁠ Brands are capitalizing on shoppers’ desire for novelty and the fear of missing out, releasing limited-edition items in small quantities, spurring wait lists and sharp premiums on resale sites.⁠ ⁠ “Each version or color, we get another little boost of dopamine,...