For the two (continuous) predictor example the deterministic component is in the form of a
plane which provides the predicted (mean/expected) response for given predictor variable
value combinations. Thus if we want the expected value for the specific values x1 and x2, then
this is obtained from the orthogonal projection from the point (x1,x2) in the plane to
the expected value plane in the 3D space. The resulting Y value is the expected value from
this explanatory variable combination.