What does Proverbs 21:9 mean?

Once again, Solomon notes the stress and misery caused by an argumentative, negative wife (Proverbs 19:13). Ancient homes, in Solomon's era, often had flat roofs accessible by stairs. In both a literal and figurative sense, Solomon is referencing the stereotypical image of a man who would rather be cold, alone, and uncomfortable than inside with a wife who "nags" and finds fault.

The phrasing here is literally about a woman bringing grief to a man, but the principle applies to either spouse. Harmony and helpfulness are the ideal for any marriage, but tempers and personality conflicts can disrupt that partnership. When one's spouse is constantly complaining, arguing, or bringing insults, the other spouse suffers a great deal of stress and anxiety.

God created the first woman, Eve, to live in harmony with her husband Adam. He created her to be a helper and treasured partner (Genesis 2:18). The apostle Peter exhorts wives to adorn their hearts "with the imperishable beauty of a gentle and quiet spirit, which in God's sight is very precious" (1 Peter 3:4). With equal importance, God called on husbands to love and sacrifice for their wives by following the example of Jesus Christ (Ephesians 5:28).

The exact same statement is repeated in Proverbs 25:24.