From Osher Doctorow

Look at (1 + y - x)(1 + u - v):

1) (1 + y - x)(1 + u - v) = 1 + y - x + u - v + uy -xu -vy + xv

Here the one-variable terms 1 + y - x + u - v have the correct signs
since negative signs indicate causes and positive signs indicate
effects. This is absent from the complex form (x + iy)(v + iu) and so
one can say that although it is "implicit" in the complex product, it
is not explicit. The two-factor terms uy - xu -vy + xv have what
should be the negative sign of xv (product of the causes) positive (+
xv) because the product of two negatives is positive, so it does have
to be "decoded" with the explicit rule that in two-factor terms the
one-factor term (-x and -v) determines the causation (xv being causal).