I read this view in a commentary recently. It seems like a plausible explanation of how Saul failed and David succeeded; the trouble is that it's not exactly what the Bible says.
1 Samuel 9:15-17, 21; 10:1
Actually, what I said is based on scripture.
1) There was a Benjamite, a man of standing, whose name was Kish son of Abiel, the son of Zeror, the son of Bekorath, the son of Aphiah of Benjamin. 2 Kish had a son named Saul, as handsome a young man as could be found anywhere in Israel, and he was a head taller than anyone else. (1 Samuel 9:1-2)
2) About this time tomorrow I will send you a man from the land of Benjamin. Anoint him ruler over my people Israel; he will deliver them from the hand of the Philistines. I have looked on my people, for their cry has reached me. When Samuel caught sight of Saul, the Lord said to him, “This is the man I spoke to you about; he will govern my people.” (1 Samuel 9:16-17)
3) “You have done a foolish thing,” Samuel said. “You have not kept the command the Lord your God gave you; if you had, he would have established your kingdom over Israel for all time. But now your kingdom will not endure; the Lord has sought out a man after his own heart and appointed him ruler of his people, because you have not kept the Lord’s command.” (1 Samuel 13:13-15)
4) When they arrived, Samuel saw Eliab and thought, “Surely the Lord’s anointed stands here before the Lord. ”But the Lord said to Samuel, “Do not consider his appearance or his height, for I have rejected him. The Lord does not look at the things people look at. People look at the outward appearance, but the Lord looks at the heart.” (1 Samuel 16:6-8)
Saul was anointed king at the people's preference, David was anointed king as one after God's heart.