The transition from college to the NFL is notoriously difficult for rookie quarterbacks. That's especially true when you are learning a much different offensive system than you worked under in college.
"The Stanford offense has a lot of the West Coast ideas in it," Luck said via the Indianapolis Star. "So all of the terminology was West Coast. (Colts offensive coordinator Bruce) Arians' offense is not West Coast, so it's learning a whole new thing. It's not too bad, and practice reps help."
The Stanford system took advantage of Luck's biggest strengths: his athleticism, accuracy, and quick decision making. Arians system -- honed in Pittsburgh of late -- relies more on deep throws. The difference between the two systems has not been talked about much, but it could make Luck's introduction to the league even tougher.