I use a regression as my predictor. Let's say my regression is
(y=a1 x1 + a2 x2 + a3 x3)
y=a_1 x_1+a_2 x_2+a_3 x_3
I realized that in practise, when my prediction is way off, it's usually because one factor significantly skewed the prediction. For example, x1,x2 are both slightly negative...