The L.A. case is the first to make it to trial. It is scheduled to last about six weeks, and it  focuses heavily on Meta—in particular, Instagram. (The defendant originally included TikTok, Snap, and YouTube. TikTok and Snap settled with the plaintiff last month rather than go to trial. YouTube remains part of the case, though it is less central to the complaint. The company has said that allegations against it are “simply untrue.”) The lawsuit asks an existential question about Meta’s business: Can the fundamental design and most basic features of Instagram directly cause mental-health problems in kids and teenagers? The jury will be asked to answer that question, and Meta is taking a big risk by allowing it to do so (though it can appeal to a judge if it loses).