One idea is that he's all about the money -- even though he may lead the league in endorsements declined.
Another idea is that he is not very competitive -- even though he has been fending off skeptics with hard work and great play for half a decade.
Another idea suggested here and there is that he's not worth a medium-sized NBA contract because he's not that good of a player, especially on defense.
Here's where the whole project starts to reek of revisionist history. My two cents:
Jeremy Lin IS a risk because he has played at an elite level for only 886 minutes, and everything about that has the chance to be a little fluky. Regression to the mean can hurt.
Jeremy Lin IS a risk because after that short stint playing long minutes, he was injured. It seems a little nuts to project his health for the next 246 regular-season games (three seasons, or the scope of his next contract) when he was shelved after his first 26 games of regular playing time. With Greg Oden as my witness, some bodies aren't meant for the NBA grind. There's no special reason to suspect Lin will have trouble, but you'd feel better if he had 200 NBA games under his belt.
Jeremy Lin IS NOT a risk because during the 26 games of Linsanity he didn't play very well. The simple truth is that, even if you count in his bad games, he was tremendous.