The story of David and Goliath set the standard for the underdog.
However, the full story of David is a complex story because David was a complicated man. His life was full of conflict, pain, and suffering; and at the same time his life was full of joy, blessings, and God's favor.
The harp in his hand represented his love and praise for the Lord.
The sling in his hand represented his success as a warrior.
The caves in his life represented the dark seasons.
The crown represented the victories in his life.
He was the object of parades, with women singing songs of his military accomplishments; and yet he witnessed half of the nation turn against him, including the betrayal by one of his own sons.
His greatest enemy was the prior king, and his best friend was that king's son!
He saw one of his children rise to great accomplishments and great renown (Solomon); while another child went down in history as a traitor (Absalom).
He had strong faith and trust in his God but was weak when it came to beautiful women.
He was a leader on the battlefield, but a failure as a father and husband.
But, through it all, David somehow maintained his relationship with Almighty God and was known as a "man after God's own heart". (1 Samuel 13:14)