Bullpen depth and reliability
If there was anything that stood out the most, it was the disastrous performance by the bullpen. After having a reliable closer in Wade Davis leave for Colorado, the Cubs went to Brandon Morrow, who missed time due to an injury. Injuries hurt the bullpen and the lack of production hurt the development.
Even though according to ESPN.com, the Cubs at the end of the end of the regular season ranked third overall in the league in pitching, it was a struggle to watch at times. They blew 19 of their 65 save opportunities according to ESPN. The Cubs need to add a left handed reliever that can be reliable.
With Zach Britton resigning with the Yankees and Andrew Miller signing with the Cardinals, the market for left handed relievers is very slim. However, look for the Cubs to add one during the trade deadline. Aroldis Chapman was acquired during the trade deadline.
Morrow and Strop missed time, and Edwards along with Justin Wilson struggled to be reliable relievers. The Cubs need to add a left handed reliever, who is reliable, they need Edwards to have a comeback year, and Morrow needs to stay healthy.
These are the three key reasons on how the Cubs can win a World Series without Bryce Harper.