Of course the human intellect is prerequisite to predict and decide about the market however there are speculations (results drawn from the computation of market data and intellect) backed by the signals and speculations not backed by signals.

In many cases, people are unable to understand and differentiate between the two. Though their concepts about an issue are most of the time right but the absence of market signals lead them astray. So yes one must trade only by following the market signals and drawing results from it using mind.