The Cubs think Jake Arrieta can get even better than he already is.
Yes, seriously - a guy with 18 wins on Sept. 5 and a 2.03 ERA can get even better.
Arrieta is a fitness freak, with an incredible work ethic that has drawn awe from everybody around him (remember Joe Maddon's money quote about Jane Fonda's workout tapes?).
The 29-year-old ace has seen his career take off since being traded to the Cubs in July 2013, but where is the ceiling? How high can he fly?
Even he's not sure.
"I don't know how good I can be," Arrieta said after shutting down the Diamondbacks in Saturday's 2-0 victory.