"Consistency" is the second-most misused word in sports.
(The most misused word in sports is "athleticism," which manages to be tautological and vague at the same time. Cam Newton used his "athleticism" to make a great play? Well, what else is he going to use? And why not describe how it's different from how Maurice Jones-Drew or Jordy Nelson or Von Miller use their skills to make great plays? But anyway.)
When fans or analysts or coaches say a player needs to be more consistent, what they almost always really mean is that he needs to be better. Think of an athlete who drives you crazy with what you perceive to be his maddening inconsistency, and check out his stats. You'll probably find they're more alike from year to year than you imagined, just not good enough to win as many games as you'd like. Mark Sanchez has thrown for between 5.6 and 5.8 net yards per attempt (which factors in sacks) in each season of his career. Dwight Howard has hit 58.6 percent to 59.6 percent of his free throws every season since 2005. A.J. Burnett's numbers in 2011 were just about identical to those he posted in 2010. Consistent!