A market is essentially a human swarm of traders and investors. As such, markets are prime candidates for intelligent emergent behavior. Emergent Behavior (EB) is recognized by some experts as "a defining property of complex systems," and "an almost inevitable consequence of any multi-agent system." Some don't believe that humans have "the natural ability to form a swarm intelligence" (Unanimous.ai). We believe the evidence within markets themselves prove otherwise.
Even if all markets did was trend, that alone would be strong proof of swarm behavior. But markets do much more than trend! They count themselves. They define specific values and then use those values to manage movement and shift direction. They can signal observers in ways that have only recently been discovered. They can recognize multiples of a number. They can add, multiply, divide, and create meaningful numeric relationships. Even volatility is tied to numeric meaning in markets. Any intelligent system needs a memory. Markets have short and long-term memories and can re-hit an exact price level, minutes, hours, days, weeks, and even months and years later. Everything markets do is about creating internal meaning.
Unfortunately, markets are not seen as the information generators that they are. Due largely to the financial media, they are instead viewed as systems that require a constant influx of events in order to move.
Lastly, EB is not mass sentiment or mass psychology. Think of it as a "brain of brains," the emergence of a true super-intelligence. Just as billions of neurons within a single brain create consciousness, millions of brains active in a market produce something larger than the parts. You cannot trade as you should, without understanding how the market mind thinks. And the manifestation of its thinking, is price action.