In Biblical numerology, he number "five" is for grace. I like to think that GOD'S grace was there and sufficient for whatever David was to face. It was proven to be so. Have you ever thought about the how accurate the stone was directed to the exact place that wasn't protected or notice that Goliath fell forward, "and he fell upon his face to the earth", instead of backward when hit, ever wonder if GOD may have given him a push into the stone? David told him, "This day will the LORD deliver thee into mine hand,...that all the earth may know that there is a God in Israel." I think this is a great story.