When I was a kid, I was a militant atheist. I got bullied and bored at Sundays School, found the stories I was told somewhat implausible - even at that age I knew that people don't really walk on water - and when I was six I told my mother I didn't believe in God. So that was the end of religion, for many years.
One of the stories I objected to was that of David and Goliath. Come off it, people don't really grow to six cubits and a span, or about nine feet nine inches (1 Samuel 17:4). I've occasionally heard fundamentalist preachers tying themselves in knots with dubious attempts to convince congregations that this was possible, but one of the advantages of being a Methodist is that people are far too sensible to take any notice of the nonsense they hear from preachers. I am a preacher, so I can say what I like about them!
Then there's a different story in 2 Samuel 21:19, where Goliath is killed by a man named Elhanan. There's no detail, it contradicts the well-known, romantic version of his demise, and anyway we all know that the Bible can't possibly contradict itself, or the sky will fall. So it gets ignored.
I never took much notice of the tale till I got a copy of 'The Dead Sea Scrolls Bible' (Abegg, Flint & Ulrich, 1999). It gives a translation of the Biblical material from the Dead Sea Scrolls. The Hebrew manuscripts traditionally used as the basis for our translations are medieval; the earliest complete copy of the Old Testament is 9th Century. The DSS are from around the 1st or 2nd Century BC, and get us far closer to the 'original' text. It gives Goliath's height as 'Four cubits and a span' or about six feet nine inches. This is massive, especially for a time when people were far less well-nourished than today, but not beyond reasonable bounds. Men of similar size are reported from the ancient world; according to the Historia Augusta, for instance, the Roman emperor Maximinus Thrax was well over eight feet high. It's not a reliable source, but no doubt he was extremely large. When 'Little John's grave' at Hathersage in the Peak district, was opened in 1784, they apparently found a human thigh bone 32 inches long, which would make the occupant at least seven feet tall. I say nothing about the historicity of the Goliath story.
Of course, the Hebrew wasn't the only version of the Hebrew Scriptures circulating in the ancient world. There's also the Septuagint, a Greek version produced some time after Alexander conquered the world, or at least the bit of it known to the Greeks. The earliest manuscripts, from the 2nd or 3rd Century AD, make Goliath four cubits and a span, the same as the DSS. Manuscripts from a little later make him five cubits, and medival ones, six cubits and a span. You couldn't have a better example of copyists 'improving' a text.