Seven Things Characterize A Stupid Person, And Seven A Wise One. A Wise Man Does Not Speak Before One Who Is Greater Than He In Wisdom Or In Years; He Does Not Interrupt The Words Of His Fellow; He Does Not Rush To Answer; He Asks What Is Relevant To The Subject Matter And Replies To The Point. He Speaks Of First Things First And Of Last Things Last; Concerning That Which He Has Not Heard, He Says, "I Have Not Heard," And He Acknowledges The Truth.

And The Reverse Of These Characterize A Stupid Person.

Concerning That Which He Has Not Heard, He Says, "I Have Not Heard"

In his commentary on this Mishnah, Rashi (and similarly, R. Ovadiah of Bartenura) interprets this as referring to a wise man's reluctance to render a halachic decision based on only his own reasoning. Unless he has heard a ruling from an authoritative source, he refrains from stating his opinion.

Without discounting Rashi's view, it is also possible to interpret the mishnah's statements simply: a wise man is not ashamed to admit his lack of knowledge. He has the humility to acknowledge the limits of his wisdom.

(Likkutei Sichos, Vol. XVII, p. 110)