Well, of course they can...all they have to do is do it.
But you know what we really mean. The Cubs' overachievement in '15 (close to ten wins when factoring in PWP, non-save good fortune, and other events) is suggesting to some that adding John Lackey, Jason Heyward and Ben Zobrist has put this team in the stratosphere.
What the Cubs are banking on is that Heyward, who's struggled against lefties for most of his career, is over that problem after a decent showing last season. That remains to be seen.
The fact is that most NL teams really struggle when they bat their left-handed hitters against southpaws. The Cubs masked that last year by minimizing those plate appearances, with a solid plurality of them going to Anthony Rizzo, who performed well in those situations (.294/.409/.472). Rizzo pretty much singlehandedly put the Cubs into the top half of NL teams in terms of their LHB performance against LHP.
This year, however, the Cubs seem committed to trotting out more lefty hitters against southpaws. Heyward and Keith Schwarber (.481 OPS vs southpaws) are the major names here. The Cubs expect Hayward to hit better against lefties than Chris Coghlan did last year, but the question is by how much.
The Cubs do have the option of playing Zobrist in left against lefties while giving Javier Baez some time at second base. The jury is still out on Baez, however.
So when we factor all that in, we see the Cubs at best holding even with their actual quality level from 2015--86-87 wins. To offset that, they'll need an uptick in Year Two from Kris Bryant (as opposed to a sophomore slump) and/or a step-up from Jorge Soler. And these two will have to be part of the punishment for opposing lefty SPs in order for the Cubs to come close to matching their 2015 record against lefties (20-14, with six of those wins coming in games where Chicago scored two runs or less).