Duncan is a person who prioritizes his own privacy. That means keeping things such as how he really feels about things to himself, although Rah-Kah is good at telling when he is troubled. The exception is when he is directly insulted as he is rather quick to a fight if he feels like he could win it.

He isn't stupid and has a strong drive of self-preservation, and unfortunately, that does mean he turns his back on others. He finds sharing emotions a waste of time and is terrible at comforting others. He is selective on what rules he decides to follow, and values what he deems 'fair' over things such as... 'legal'.

That being said, he is a person who stands by his word, no matter what. It is one of the few good lessons he learned from his father. 'No one buys from the ship with no wind, reputation is everything'. When facing others, he can be highly distrusting of everyone around him, he is blunt and hardly sugar coats things as he is a bit oblivious to the feelings of others. However, when drinking he is a 'emotional' drunk who is very open about his feelings. 

He has an overall cynical view of the world and thinks everyone is ultimately out for themselves. That being said, he has a lot of room to grow as a person and he finds himself often changing the more time he spends with Fi.