Contradiction in the Bible?

I was reading my Bible when I came across 1 Samuel 15:35. It says, "And Samuel went no more to see Saul until the day of his death. Nevertheless, Samuel mourned for Saul, and the Lord regretted that He had made Saul king over Israel." To me, the word regret sounds like God made a mistake. I would like to hear specifically from Christians who believe that God is perfect what they think that that word "regret" means. Because if God made a mistake that causes a lot of big problems and I want to know what you think about that especially if you believe that he doesn't make mistakes.