2 Samuel 10 - Here's a chapter in the Bible where a valuable lesson can be learned. When the king of Ammon died, David sent an envoy of men to comfort the king's son. People in Ammon made their king think these men were actually spies and the king treated them shamefully, bringing a war on his people. He found out that David and the men of Israel were far stronger and they were soundly defeated in spite of calling for help from Syria. The lesson is not to assume the wrong thing and bring needless trouble upon ourselves. David was genuinely seeking to show kindness, but he wouldn't be treated with contempt.
1 Chronicles 19 - The same event of 2 Samuel 10 is recorded here. The way David's envoy of kindness were treated shows the contempt the son of the king of Ammon had towards David. David's men were treated with shame and humiliation, not just having their garments cut off at their waist, but having their beards shaved. Utter contempt was shown. David's response showed that he understood the threat Ammon would pose against Israel. Ammon faced defeat from David's forces, giving up the opportunity to become a friendly nation to Israel.
Psalm 20 - David sought help from God when trouble came. He found the Lord always there for him. Verse 4 is one of those verses people love because it shows God's willingness to grant our desires. But, it should be understood that our desires should be first to please God for that would govern what kind of desires we would have in our hearts.