But if ye will not obey the voice of the Lord , but rebel against the commandment of the Lord , then shall the hand of the Lord be against you, as it was against your fathers.
1 Samuel 12:15 KJV
http://bible.com/1/1sa.12.15.KJV

God was not accepted as the King at that time. They worshipped man-made gods. And because worshipping these gods is a sin, Israel was defeated by their enemies. They recognized their mistakes and promised to serve if God will deliver those enemies unto their hands. And God did as they say but still they asked for another thing from Him, to give them a king. And God did as they say once again and appointed Saul to be their King.

The Lord reminded them of obedience to the one He had appointed. Israel asked and God gave it to them. One condition for it was obedience.

Often we ask God for what we want - our dreams, plans and needs. But we stay disobedient and end up disappointed. We experience failure. But it is the consequence of our actions that we are reaping just like the numerous defeats of Israel because they chose to disobey. When we ask Him for our heart's desire He also asks us for our faithfulness so we will obey His commands and instructions. God wants what is the best for us so following and obeying His commands will not lead us to failure or anything negative, but it will lead us to our answered prayers.