There is not question that King David was a brilliant warrior. Repeatedly he overcame great odds but in 1 Chronicles 21 he did something that was a big mistake. He decided that he would take a census of how many fighting men there were at his disposal. Taking a census of his potential  army at first sounds like a sound decision but you have to consider the whole picture.

1. The idea to number the people was not originally David's but Satan. "Satan rose up against Israel and incited David to take a census of Israel." 1 Chronicles 21:1 Sometimes when we make decisions, we need to check our motives and if the decision is in God's will. 1 John 5:14-15
2. He refused the counsel of his military advisors. 1Chronicles 21:3 God has placed people in our lives that we might seek their counsel.
3. If we analyze this passage, it becomes clear that David was proud or at least ambitiously curious. David was relying on his strength and not God's. When we try to govern our lives in our own strength and wisdom; we are heading for trouble.

Years later, David's son, Solomon, penned some of the best advise we can use to direct the course of our lives: "Trust God from the bottom of your heart; don’t try to figure out everything on your own. Listen for God’s voice in everything you do, everywhere you go; he’s the one who will keep you on track." Proverbs 3:5-6 [The Message}