How does he answer before hearing?
R. Yonah: Pride is among the ways of Iveles. Answering before hearing [the entire matter] shows haughtiness. He is sure that he understands the speaker before he finishes. This is folly and pride; it is shame, when it is revealed that he did not understand his friend's words 1 .
Malbim: Among the ways of Chachmah is to answer only a clear matter - "say to Chachmah, you are my sister" (7:4) - if the matter is as clear to you as your sister, [that she is forbidden to you, say it. If not, do not say it! - Shabbos 145b] Therefore, one must hear the questioner's claim and all sides of his doubt, and give a clear decision. Via this, the listener will honor him. If one answers before hearing all sides of his doubt, he will answer Iveles, i.e. Safek, and the listener will disgrace him.
Bava Basra 98b: The lowliest thing is a Chasan who lives in his father-in-law's house. Worse than this is a guest who invites other guests. Worse than this is one who answers before the other person finished speaking - "Meshiv Davar b'Terem Yishma
