Humility is knowing that the LORD is righteous and right in what He does. It is saying, "Lord, you are right to do this to me," rather than, "Lord, why are you doing this to me?" or "Lord, this isn't fair."
God sent the Egyptian king Shishak as a conqueror over King Rehoboam, in response to Judah's disobedience.
"Thus says the LORD, 'You abandoned me, so I have abandoned you to the hand of Shishak.' " Then the princes of Israel and the king humbled themselves and said, "The LORD is righteous."(2 Chron. 12:6) ESV
Finally humbled, the people saw that God was right to send Shishak. They deserved nothing better and agreed with God.
Before I can beg for God's mercy, I must humbly declare He is righteous in what He does. I don't deserve a Redeemer. There is nothing good in me. But Christ is my Redeemer and I boast only in the cross.
What happened to Rehoboam? Read 2 Chronicles 12:7ff.