Who said Saul failed? Saul and his sons had their successes with the Lord. And for all the things Saul did to David, David knew and respected Saul's calling as "the Lord's annointed".
But Saul did some things he shouldn't have done and disobeyed God's command (1 Sam 13). God knew Saul would be disobedient yet He still annointed him king. God created Saul and purposely raised Saul up to do exactly what He wanted him to do. There isn't "success" or "failure" with God.
I would think this principle would be refreshing to understand. God has choosen and redeemed us knowing we will goof up. But success and failure in carrying out God's plan doesn't rest with us. Our failures doesn't affect God's perfect plan or will or the thing He has called us to do in carrying out His plan. Because of His divine gifts all Christians will be successful for what God has called us to do. But our failures along the way only limit the blessings God wants to bestow on us and grieves the God who desires to give us His blessings.
BTW-It also should be noted that God sent kings up to fail as well but Saul was not such a person.
"Who said Saul failed?"
God. God said He was sorry He made Saul king, you disagree?
If you can't see that making God grieve over you is "failing", then there is no point in discussing anything with you. Saul made God grieve. In my book that is the definition of failure. I suppose you'd call it "success"?