In the Bible's re-collection of Saul, Saul was a man chosen by God, but later rejected because of his disobedience to the word of God. Saul was one to do what please his followers and himself.
Saul's appointment as King of Israel came when Samuel who was a prophet in Israel made his sons judges over the people. His sons walked not in his ways, but turned aside after lucre, and took bribes, and perverted judgment. This led to the elders of Israel calling for a King to lead the people, though it was not what God wanted.
Saul was therefore chosen by God to be that King, and he was anointed by Samuel. After anointing him Samuel then offered Saul certain instructions, as follows:
1Sa 10:8 And thou shalt go down before me to Gilgal; and, behold, I will come down unto thee, to offer burnt offerings, and to sacrifice sacrifices of peace offerings: seven days shalt thou tarry, till I come to thee, and shew thee what thou shalt do.
1Sa 13:8 And he tarried seven days, according to the set time that Samuel had
appointed: but Samuel came not to Gilgal; and the people were scattered from
1Sa 13:9 And Saul said, Bring hither a burnt offering to me, and peace offerings. And he offered the burnt offering.
Samuel then arrived as soon as the burnt offering was offered up, and was angry with what Saul has done. It doesn't seem from the text that Samuel was angry because Saul didn't wait the period of seven days, because it seems Samuel came later than expected, but he was angry because Saul offered up the burnt offering, which he had instructed that he would have done.
As a result of this, his Kingdom upon Israel was not establish forever because he did not follow the commandment of the LORD.