Figure 2-43. Incorrect: there is nothing in the image that explains the angle of the shadow
Figure 2-44. Correct: a shadow that stays on the horizontal, regardless of the object angle changes
There are a variety of common shadow mistakes; in this section, I'll go over a few and give you some tips on how to avoid them.
Always make sure a shadow stays put on the ground in a horizontal fashion, regardless of how the image angle may change. Notice that in Figure 2-43 there is no mountain or wall to explain the position of the donut's shadow. In Figure 2-44, the donut is hovering at an angle, but the shadow correctly "sits" horizontally on the ground. The only time the angle of a shadow would change is if the shadow hit an object that is on an angle, like a wall or mountain.
Figure 2-45. Incorrect: negative-looking shadow not on a multiplied layer
Figure 2-46. Correct: shadow on a multiplied layer
Creating your shadows on a normal, unmultiplied layer makes the shadow appear to have a "negative" effect because ...