Why did Caleb promise his daughter’s hand to the one who conquered Kiriath-sepher?

Judges 1:12 (ESV)

12 And Caleb said, “He who attacks Kiriath-sepher and captures it, I will give him Achsah my daughter for a wife.”

This was to guarantee that Achsah would have a worthy husband, and Caleb have a son-in-law who shared his faith and courage.