Answer by Raakhee Venugopal:
Arjun was predominantly moody. He is often portrayed as the quiet brooding hero of the story. His affections were channeled towards his mother, whom he considered as the center of his Universe. Nowhere in the Mahabharata can you see Arjun being described as frolicking or laughing boisterously. He kept to his world, and the only person who could pull him out of his own world was Krishna.
He was very focused and his foresightedness was legendary. This can be seen in the many incidents where he showed exemplary levels of skill in archery…at the Gurukul, at Draupadi’s Swayamvar, all those battles, big and small.
He gave a lot of importance to honoring promises…whether it was something he had committed to or whether it was aiding in the upkeep of another’s word. He agreed to share Draupadi with his brothers to honor his mother’s word. He swore to kill Karna to avenge the insult he heaped on Draupadi, and he did it. He left on a year-long exile for breaking the promise the brothers had made at the time of their marriage to respect each other’s privacy. There are several such incidents.
Arjun showed strong signs of insecurity at different instances. He is often portrayed as an individual filled with self-doubt. This trait of his first showed at his being uncomfortable with the entry of Ekalavya. And this came out in full force at the battle of Kurukshetra where he is said to have broken down into tears. Again, it was only and ONLY Krishna who was able to pull him out of this. It was not an insecurity related to his skills at warfare. Arjun was mighty proud of it. His pride often slipped into the territories of arrogance at times. And Krishna would put him in his place in the best way possible.
These are all I can think of now 🙂 Will update with more when I think of something else.