Predicting baseball is really, really hard. Very hard. There are thousands of different variables to consider, and even when you've considered all of them, sometimes a player will do something completely different just to mess you up.
Projection systems are a way to try and remove all of the emotion out of predicting, instead focusing on cold, hard numbers. They try to correct for outliers and focus on smoothing out the effect of luck, both good and bad. Ultimately, projection systems as a whole are reasonably accurate and a great way to evaluate players.
And yet. Sometimes, projection systems miss so, so hard.