Smart FOs never assume that on whole the squad will play to their projections. They work night and day to cover worst case scenarios because this is real life, not a projection. The Sox just assumed Eloy would put up 5 WAR, Moncada would stay healthy, Robert was a 7 WAR MVP and so on and on and on.
Well guess what -- if they had planned for a scenario like this they'd still be in a great position. But, a failure to plan results in failure usually.