Merck is the latest company to weather bad news in the Alzheimer’s drug race, halting a late-stage trial yesterday in an experimental amyloid-targeting candidate called verubecestat after a data monitoring committee said there was “virtually no chance of finding a positive clinical effect,” Reuters reported. Merck shares got hammered in after-hours trading Tuesday evening and during the early morning rush, but had fully recovered by mid-morning. (The stock is actually at a 52-week high now.)

Who knows? Maybe savvy traders expected the rotten news. After all, Merck simply joins a growing fraternity of pharma and biotech companies that have tried to tackle this insidious disease and failed.

Eli Lilly, of course, went through Job-like setbacks with another drug targeting (in a different way) beta-amyloid, the bits of sticky protein that clump together around nerve cells and which may block signaling in the brain as well as do other damage. In November, the company announced that the results of a Phase III trial of solanezumab “were not what we had hoped for.” Lilly had spent 15 years developing the drug and many experts believed it would be first to the gate in securing an FDA approval for slowing Alzheimer’s progression. (In full disclosure, we at Fortune had predicted—in our ordinarily can’t-miss, fail-safe, never-wrong “Fortune Crystal Ball” for 2016—that “sola” would succeed. It has now joined a scrap heap of other would-be brain-saving blockbusters (and missed Crystal Ball predictions).

The bulk of research scientists working on Alzheimer’s have long believed that a buildup of amyloid “plaques” is central to the disease’s development—and that therefore targeting this protein is the best chance for a cure. But the failure of so many efforts here has made many wonder—or wonder more loudly than ever, I should say—if that age-old thesis is wrong.

It wouldn’t be the first time. See “Galileo, solar system, 1632.”

For anyone who wants to read the best damn feature out there on this debate—and on the epic story of the effort to find a worthy Alzheimer’s drug—I recommend this 2015 Fortune classic by my colleague Erika Fry: “Can Biogen Beat The Memory Thief?”