Depending upon which version of the Arthurian legends one is reading, there are a number of different plot points in the narrative that might convey Arthur's heroism. Le Morte d'Artur by Christopher Mallory is one of the earliest and most common version of the story, and became the basis for a number of film versions, including the well-loved Excalibur directed by John Boorman. In this version of the narrative, soon after pulling the sword from the stone, Arthur leads some of his followers (who are already warriors and knights) in battle against King Leodogrance (who, after his castle is overcome, later swears loyalty to Arthur, and introduced him to his daughter Guinevere, whom Arthur later marries). Arthur is still young but as a squire to his half brother Kay, he learns about knighthood and swordsmanship. When Sir Uriens refuses to swear loyalty to the "boy king" because he is a knight and Arthur is merely a squire, he gives Uriens the sword Excalibur and asks Uriens to make him a knight. Though Uriens is tempted to keep this powerful, magical sword, there is a suggestion that whoever bears the sword can only use it to do the right thing; he knights Arthur and immediately swears his loyalty to Arthur, praising his bravery.
There are some modern novelizations of the story also, including the series by author T. H. White that begins with The Sword in the Stone, published in 1938. This novel focuses on Arthur as a boy who has his coming of age due to the destiny he realizes as a young king. Along the way he receives teachings from Merlin, and one task Merlin assigns him is to spend the night alone in the forest. Arthur is at first very afraid of the sounds in the dark and the wild animals he fears may harm him. But he gradually becomes used to what he hears, his night vision improves, and he learns to appreciate what he can learn from the forest: this could be seen as his first act of heroism, in which he realizes his own courage.