“Let us not concur casually about the most important matters.” (Kahn 11, DK & S 47, W 5)
Heraclitus is well-known to be skeptical of the majority to reach sound judgment or to become wise. He here indicates the need for careful deliberation about important matters.
Deliberation of course requires tools of “good inquiry” spoken of in Fragment 9 — for example, an intention to reach truth and a mode of inquiry that is adequate to the task.
From Heraclitus’ general writing we see that he recognizes that decisions are too often made based on a non-reflective mob mentality, at times almost spontaneously. Or he mentions, for example in the next text, the possibility of a reliance on custom or tradition alone. But a social order emerging from the former type of concurrence will be at best an assemblage of individuals who live according to private purposes, not a collectivity of individuals that recognizes a common purpose. A social order based on non-reflective dogma will be slavish. Here Heraclitus admonishes us not to settle for nonreflective opinion on important matters but to engage in sound thinking.