Having trouble zeroing in on the object ball? Can't see the contact point that, once struck, will send the object ball along the desired trajectory? Maybe the principle of Bisecting Boxes will help bring things into focus for you.
Imagine lines drawn at 90 degree angles from the long and short rails to the edge of the object ball. (See illustration) Close the box by drawing lines from the adjacent points on the rail to the point of intersection at the targeted pocket. The desired path of the object ball coincides with a diagonal line that bisects the box. The line also cuts through the object ball clearly indicating the desired contact point.
This principle applies to all shots. If you have been having trouble sighting object balls, the next time you're practicing try visualizing the box and the bisecting diagonal line to the target. With practice, it will become second nature. Your shot-making will improve exponentially.