2. Aggression - Call it the optimism of youth, but Wei Yi always believes he can win till the very end.
3. Psychology - Magnus is a great player, but most players lose to him before a single move is made because they're afraid of him ! This could be seen best in Karjakin's match against him in Bilbao. Even Nakamura who won was reluctant to feel too confident about his victory (perhaps because he's afraid of the next match). But, this Chinese kid is afraid of nobody. He's not in awe of Carlsen, and I believe he has the ability to challenge Carlsen soon.
The junior number one, Richard Rapport may have a chance too, for the same reasons as Wei Yi.
1. Age - He is only 17 years old and will get better with age. His rating is similar to Magnus' at the same age. Magnus will slowly have to deal with the pressure of playing as champion, rather than fearless challenger. By the time Wei Yi challenges Magnus, he'll be around 21-22 and Magnus will just be entering his 30s.
2. Aggression - This kid is extremely aggressive and always plays for the win.