I have previously covered four undesigned coincidences that together show that the miraculous feeding of the five thousand that is retold in all four Gospels is a historical event; Why Philip?, Green Grass and Miracles, Counting to a Miracle, and The Proof is in the Woes. There are undesigned coincidences in the Old Testament as well. Let's have a look at one!

In 2 Samuel 15–17, Ahithophel, a trusted advisor to King David, defects to join Absalom's rebellion. Ahithophel’s counsel was highly valued, "as if one consulted the word of God" according to 2 Samuel 16:23. His betrayal was significant, as he offered strategic advice to Absalom, including a plan to pursue and kill King David:

2 Samuel 17:1–4:

"Moreover, Ahithophel said to Absalom, “Let me choose twelve thousand men, and I will arise and pursue David tonight. I will come upon him while he is weary and discouraged and throw him into a panic, and all the people who are with him will flee. I will strike down only the king, and I will bring all the people back to you as a bride comes home to her husband. You seek the life of only one man, and all the people will be at peace.” And the advice seemed right in the eyes of Absalom and all the elders of Israel."

But why would Ahithophel betray David? Well, I would assume most readers have read or heard about David and Bathsheba, but if not, you can read the full story in 2 Samuel 11-12. I highly recommend you reading it if you haven't, but otherwise a brief recap would be that David committed adultery with Uriah's wife Bathsheba, got her pregant doing so, then arranged for Uriah to die and married Bathsheba. The prophet Nathan confronted David about this, but Bathsheba is not mentioned, which puts into question if she even consented.

We also learn that Bathsheba's father was named Eliam.

2 Samuel 11:3:

"And David sent and inquired about the woman. And one said, “Is not this Bathsheba, the daughter of Eliam, the wife of Uriah the Hittite?”"

And who was Eliam's father? In a completely different context, we read the following.

2 Samuel 23:34:

"...Eliphelet the son of Ahasbai of Maacah, Eliam the son of Ahithophel the Gilonite..."

Ahithophel!

Ahithophel was Eliam's father, and thus Bathsheba's grandfather! This is not alluded to at all in the narrative about his betrayal of David, but gives a very plausible explanation for why he would betray David! It's the typical kind of undesigned coincidence that one would expect to find in historical narrative, and would not expect to find in made up stories.