I think it may be one of two things.
1. Maturity, some people think he may be immature, even for his age
2. Effort, he will not be able to shake the Derrick Coleman comparisons until he accomplishes something of worth in the NBA. People still say how easy the game comes for him, but they don't realize that he works, and as we know he lead all D1 in rebounding, lazy players generally don't lead anything in rebounding.
These are guesses by me I am not a draft "expert" like Chad Ford, I certainly don't agree with them. Also it should be noted that immaturity and work ethic is considered character by some. The term "character issues" have come to infer something else in sports these days, like who he shot, who he took money from, how many kids he has, or why he never went to class.
