There are two challenges to making a pocket billiards or pool shot:
Hitting the aimed at or “object” ball where you want to
Knowing where to hit the object ball
Hitting the object ball where you want to.
The roundness of the balls does a lot of strange things. The first one you must know to play pool well is that in most cases it is impossible to hit where you aim at directly! The curvatures of the balls causes the cue ball and object ball to collide before the cue ball can get to the spot you want to hit! See below.