In the chapter titled "The Grail" in Chretien de Troyes' Perceval; or, The Story of the Grail, translated by Ruth Harwood, Perceval does a few things to show he possesses the heroic traits of bravery, intelligence, and humbleness.
One way in which he shows bravery is through knowing his own weaknesses and when to face them. We see him face his own fears when he reaches the stream and prays to God: "Oh God Almighty! It would seem, / if I could get across this stream, / I'd find my mother, if she's living" (2991-94). We further see him show bravery when he demonstrates the ability to act when needed. For example, he finds someone raising the drawbridge and is forced to turn back to the castle just as he was about to leave the castle to cross back over the stream in order to find the squires who were checking traps and ask what they knew about the lance and the grail; he was very quick to call out and ask who raised the drawbridge. He is also very quick to call out asking the person to come and talk to him because he wanted to ask the person his questions.
We also see Perceval demonstrate intelligence when he devotedly tries to find solutions to his problems. For example, in the beginning of the chapter, he devotedly tries to find a way across the stream, even riding all the way up the stream's bank with his horse. He even acts intelligently when he has the sense to ask the two fishermen he sees if there is a way across the stream. Being able to ask for help even demonstrates his humbleness because many are often too prideful to admit they need help and to ask for it.
All in all, just as a young knight should be, Perceval is characterized as having the heroic traits of bravery, intelligence, and humbleness.