There are so many different variables at play, that forecasts miss "something" more often than not...either that, and/or they are not weighted properly into the forecast.
Example...I was able to discern that the Aleutian ridging would have episodes where it extended far enough poleward to induce some notable wintery periods by looking at past east biased la nina seasons..ie, no total blow torch rater like 2011-2012. However, I apparently did not weight the abrupt rise in solar activity that took place last fall heavily enough, so the forecast SSW/blocking never materialized. The poleward Aleutian ridging was able to compromise to a degree, but even that failed in March.
We do know from utilizing analogs of past seasons that an abrupt rise in solar activity is detrimental to blocking, but I made the decision that it wouldn't play as large a role as it apparently did. You can use analogs, and still miss...no one is implying its a "silver bullet"...it is incumbent upon the forecaster to apply and weight them correctly.