Ultimately, the chosen became the rejected. Saul was too rash, too unthinking, too disposed to decisions based on convenience, not correctness. Thus the king lost his kingdom.
When commanded by God to destroy all the riches of the Amalekites, Saul let himself be swayed by the people’s cravings for plunder.
When he was supposed to wait for Samuel to offer sacrifice, Saul unwisely performed priestly duties that didn’t correspond to him.
God revoked Saul’s kingship and gave it to David.
When you are young and immortal (tongue in cheek), you are prone to imprudence. As you grow older, (hopefully) you grow wiser. It’s a good thing to grow out of — if you live through the stupid stunt stage.