For years, the “best price” displayed in U.S. stocks could miss a better priced order sitting in the market. The reason was surprisingly simple Size mattered. Under the old market structure framework, the National Best Bid and Offer (NBBO) was built around round lot quotations. An odd lot order could be sitting at a better price without becoming part of that displayed NBBO. And odd lots weren’t some tiny corner of the market. The SEC reported that odd lots grew from about 15% of U.S. stock trades in January 2014 to more than 55% by March 2022. More than half. Yet the framework used to define the market’s “best” displayed price did not fully incorporate those smaller quotations. The SEC later changed the rules to improve transparency around better priced odd lot orders. So a trader could look at the screen and think That’s the best price available. But historically, that wasn’t necessarily the whole picture. The screen shows you the market. The rules decide what part of the market gets displayed. Sometimes the thing you can’t see isn’t hidden behind a sophisticated indicator. It’s hidden in the definition of “best.”