The folks at Freakonomics explain why Jeremy Lin's success was actually predictable:

An average point guard selected in the NBA draft from 1995 to 2009 posted a 5.8 Win Score per 40 minutes (WS40) in his last year in college.  In 2009-10, Lin posted a 8.0 WS40, which meant he was an above average prospect.

Lin’s above average Win Score was driven by his ability to excel at shooting efficiency from two-point range, his ability to get rebounds, and his ability to get steals. When we look at which college factors predict an NBA player’s productivity, we find that it is these very same factors that matter: shooting efficiency from two-point range, rebounds, and steals.

Now what factors don’t matter? We found that a player’s height, age, and other box score numbers are not associated with more NBA production later on. In addition, appearing in the Final Four – a factor that clearly impacts draft position – doesn’t suggest higher production in the future.  In sum, what Lin didn’t have in 2010 wasn’t related to his future NBA prospects.  Consequently – contrary to what people in the NBA thought back in 2010 — people outside the NBA argued (again, back in 2010) that Lin might be worth a look.  

I smell a Moneyball moment for the NBA.