It is conventional wisdom that after cross-examination has begun, lawyers should not meet with their witnesses to discuss their testimony and all substantive preparation should cease. Lawyers follow this path out of fear that the court will permit opposing counsel to inquire about the conversations. Many lawyers assume that their adversaries will also not meet with their witnesses, and therefore ask to begin their cross-examination before an overnight or lunch break.
But what is the source of this "wisdom"? And how should lawyers approach witness preparation during breaks in testimony?