Special expertise might be needed in many cases to operate the circle effectively. The circle is responsible for noticing when it might be better to ask someone for input or help. Another consideration is the effect of group think (a psychological phenomenon where too much conformity in a group results in irrational decisions). That’s where asking for feedback from outside the circle and even outside the organization is useful to make sure enough fresh ideas find their way into the circle.
For more information, check out our handbook Many Voices One Song section 4.4