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"?
Are you assuming that God's grief over something indicates His failure to bring about something He purposed to?
A Christian can grieve God (Eph 4:30) and can quench God (1 Thes 5:19), and those are momentary failures that have consequences like David’s sin with Bathsheba; but one can’t fail to carry out God’s will. Jonah grieved God by running away from Nineveh but God brought him back to do His will. Saul likewise fulfilled God’s will but God was grieved that Saul couldn’t be more than he was.
Saul failed but he had his successes as well. God looks at people as either "doing right in His eyes" or "doing evil in His eyes". The whole two books of Kings states this over and over again. King So-and-So did what was good (evil) in the sight of the Lord and then it goes into their history. There were some very good kings that did some bad things and there were some very bad kings that did some good things (Ahab humbled himself to God). But they all did what God wanted them to do. If Saul was listed in the books of Kings do you think it would say, “And Saul did what was right in God’s eyes…” or do you think it would say “And Saul did what was evil in God’s eyes…”?
Nowhere in scriptures does it say or even hint that we fail God. The only time “fail” is used is when we “fail the test” in knowing if Christ is in us. (2 Cor 13:5-6)
My flesh and my heart may fail, But God is the strength of my heart and my portion forever. Psalms 73:26