What does Proverbs 20:28 mean?

All proverbs, biblical or otherwise, are general statements. They are intended as short summaries of wisdom, and not meant to be taken as absolute rules. In this case, Solomon (Proverbs 10:1) notes that caring, faithful leaders inspire loyalty in their people. A king who is just (Proverbs 20:26) and good to his people (Proverbs 29:2) will typically be rewarded by a nation who loves and defends their king. While it's possible for good leaders to be unfairly attacked, or evil leaders to cling to power, the expected pattern is for good leaders to inspire happy, devoted followers.

The history of Judah and Israel shows what happens when kings either reign in righteousness or digress from God's standards of love and faithfulness. In 721 BC, Israel, the northern kingdom, fell to the Assyrians because it lacked good kings and the nation dishonored God. However, the southern kingdom, Judah, lasted until 586 BC because it had some good kings and periods of revival. God places rulers in authority for the people's good, but He can remove those rulers at His discretion. Psalm 75:7 says, "It is God who executes judgment, putting down one and lifting up another."